Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $190.75   5.854%   $201.9165   $201.92   $201.90   $201.90  
  Purchase #2 $100.35   6.547%   $106.9199   $106.92   $106.90   $106.90  
  Purchase #3 $215.39   13.640%   $244.7692   $244.77   $244.75   $244.80  
  Purchase #4 $188.96   8.595%   $205.2011   $205.20   $205.20   $205.20  
  Purchase #5 $127.75   12.291%   $143.4518   $143.45   $143.45   $143.50  
  Purchase #6 $193.95   13.405%   $219.949   $219.95   $219.95   $219.90  
  Purchase #7 $131.45   7.204%   $140.9197   $140.92   $140.90   $140.90  
  7 purchase totals = $1,148.60       $1,263.1272   $1,263.13   $1,263.05   $1,263.10