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 $182.80   10.462%   $201.9245   $201.92   $201.90   $201.90  
  Purchase #2 $12.26   13.216%   $13.8803   $13.88   $13.90   $13.90  
  Purchase #3 $32.38   9.658%   $35.5073   $35.51   $35.50   $35.50  
  Purchase #4 $197.35   6.252%   $209.6883   $209.69   $209.70   $209.70  
  Purchase #5 $220.58   5.180%   $232.006   $232.01   $232.00   $232.00  
  Purchase #6 $204.25   4.495%   $213.431   $213.43   $213.45   $213.40  
  Purchase #7 $122.36   5.541%   $129.14   $129.14   $129.15   $129.10  
  7 purchase totals = $971.98       $1,035.5774   $1,035.58   $1,035.60   $1,035.50