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 $86.47   12.220%   $97.0366   $97.04   $97.05   $97.00  
  Purchase #2 $178.81   11.838%   $199.9775   $199.98   $200.00   $200.00  
  Purchase #3 $111.64   6.149%   $118.5047   $118.50   $118.50   $118.50  
  Purchase #4 $165.54   3.260%   $170.9366   $170.94   $170.95   $170.90  
  Purchase #5 $231.91   6.342%   $246.6177   $246.62   $246.60   $246.60  
  Purchase #6 $31.82   10.658%   $35.2114   $35.21   $35.20   $35.20  
  Purchase #7 $169.97   11.189%   $188.9879   $188.99   $189.00   $189.00  
  7 purchase totals = $976.16       $1,057.2724   $1,057.28   $1,057.30   $1,057.20