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 $112.57   8.329%   $121.946   $121.95   $121.95   $121.90  
  Purchase #2 $145.28   7.294%   $155.8767   $155.88   $155.90   $155.90  
  Purchase #3 $66.64   13.633%   $75.725   $75.73   $75.75   $75.70  
  Purchase #4 $45.56   8.356%   $49.367   $49.37   $49.35   $49.40  
  Purchase #5 $212.74   7.639%   $228.9912   $228.99   $229.00   $229.00  
  Purchase #6 $185.82   11.403%   $207.0091   $207.01   $207.00   $207.00  
  Purchase #7 $163.41   11.536%   $182.261   $182.26   $182.25   $182.30  
  7 purchase totals = $932.02       $1,021.1760   $1,021.19   $1,021.20   $1,021.20