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 $55.50   13.822%   $63.1712   $63.17   $63.15   $63.20  
  Purchase #2 $86.93   9.416%   $95.1153   $95.12   $95.10   $95.10  
  Purchase #3 $216.84   5.801%   $229.4189   $229.42   $229.40   $229.40  
  Purchase #4 $218.98   5.483%   $230.9867   $230.99   $231.00   $231.00  
  Purchase #5 $70.60   7.629%   $75.9861   $75.99   $76.00   $76.00  
  Purchase #6 $58.51   6.728%   $62.4466   $62.45   $62.45   $62.40  
  Purchase #7 $201.30   3.201%   $207.7436   $207.74   $207.75   $207.70  
  7 purchase totals = $908.66       $964.8684   $964.88   $964.85   $964.80