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 $44.67   5.162%   $46.9759   $46.98   $47.00   $47.00  
  Purchase #2 $147.51   13.846%   $167.9342   $167.93   $167.95   $167.90  
  Purchase #3 $68.74   7.778%   $74.0866   $74.09   $74.10   $74.10  
  Purchase #4 $59.93   12.568%   $67.462   $67.46   $67.45   $67.50  
  Purchase #5 $221.32   13.834%   $251.9374   $251.94   $251.95   $251.90  
  Purchase #6 $236.87   8.286%   $256.497   $256.50   $256.50   $256.50  
  Purchase #7 $147.45   3.865%   $153.1489   $153.15   $153.15   $153.10  
  7 purchase totals = $926.49       $1,018.0420   $1,018.05   $1,018.10   $1,018.00