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 $202.45   10.332%   $223.3671   $223.37   $223.35   $223.40  
  Purchase #2 $140.82   7.552%   $151.4547   $151.45   $151.45   $151.50  
  Purchase #3 $155.58   5.806%   $164.613   $164.61   $164.60   $164.60  
  Purchase #4 $5.32   13.826%   $6.0555   $6.06   $6.05   $6.10  
  Purchase #5 $118.96   5.346%   $125.3196   $125.32   $125.30   $125.30  
  Purchase #6 $24.69   4.314%   $25.7551   $25.76   $25.75   $25.80  
  Purchase #7 $204.77   3.730%   $212.4079   $212.41   $212.40   $212.40  
  7 purchase totals = $852.59       $908.9729   $908.98   $908.90   $909.10