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 $65.86   11.386%   $73.3588   $73.36   $73.35   $73.40  
  Purchase #2 $242.84   8.829%   $264.2803   $264.28   $264.30   $264.30  
  Purchase #3 $149.27   10.663%   $165.1867   $165.19   $165.20   $165.20  
  Purchase #4 $234.92   13.182%   $265.8872   $265.89   $265.90   $265.90  
  Purchase #5 $49.26   7.552%   $52.9801   $52.98   $53.00   $53.00  
  Purchase #6 $128.73   11.327%   $143.3112   $143.31   $143.30   $143.30  
  Purchase #7 $223.65   10.675%   $247.5246   $247.52   $247.50   $247.50  
  7 purchase totals = $1,094.53       $1,212.5289   $1,212.53   $1,212.55   $1,212.60