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 $60.78   8.700%   $66.0679   $66.07   $66.05   $66.10  
  Purchase #2 $88.69   4.146%   $92.3671   $92.37   $92.35   $92.40  
  Purchase #3 $138.29   8.752%   $150.3931   $150.39   $150.40   $150.40  
  Purchase #4 $166.44   5.155%   $175.02   $175.02   $175.00   $175.00  
  Purchase #5 $153.32   11.604%   $171.1113   $171.11   $171.10   $171.10  
  Purchase #6 $11.26   8.873%   $12.2591   $12.26   $12.25   $12.30  
  Purchase #7 $167.69   11.819%   $187.5093   $187.51   $187.50   $187.50  
  7 purchase totals = $786.47       $854.7278   $854.73   $854.65   $854.80