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 $194.93   3.357%   $201.4738   $201.47   $201.45   $201.50  
  Purchase #2 $40.73   7.394%   $43.7416   $43.74   $43.75   $43.70  
  Purchase #3 $60.55   6.234%   $64.3247   $64.32   $64.30   $64.30  
  Purchase #4 $194.93   5.608%   $205.8617   $205.86   $205.85   $205.90  
  Purchase #5 $51.65   3.247%   $53.3271   $53.33   $53.35   $53.30  
  Purchase #6 $229.61   9.654%   $251.7765   $251.78   $251.80   $251.80  
  Purchase #7 $171.28   4.505%   $178.9962   $179.00   $179.00   $179.00  
  7 purchase totals = $943.68       $999.5016   $999.50   $999.50   $999.50