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 $71.71   6.609%   $76.4493   $76.45   $76.45   $76.40  
  Purchase #2 $172.44   4.850%   $180.8033   $180.80   $180.80   $180.80  
  Purchase #3 $231.59   4.714%   $242.5072   $242.51   $242.50   $242.50  
  Purchase #4 $58.26   4.588%   $60.933   $60.93   $60.95   $60.90  
  Purchase #5 $80.95   7.444%   $86.9759   $86.98   $87.00   $87.00  
  Purchase #6 $100.25   8.474%   $108.7452   $108.75   $108.75   $108.70  
  Purchase #7 $95.48   12.589%   $107.5   $107.50   $107.50   $107.50  
  7 purchase totals = $810.68       $863.9139   $863.92   $863.95   $863.80