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 $217.56   13.432%   $246.7827   $246.78   $246.80   $246.80  
  Purchase #2 $165.37   11.573%   $184.5083   $184.51   $184.50   $184.50  
  Purchase #3 $238.73   3.837%   $247.8901   $247.89   $247.90   $247.90  
  Purchase #4 $44.90   3.424%   $46.4374   $46.44   $46.45   $46.40  
  Purchase #5 $95.47   12.664%   $107.5603   $107.56   $107.55   $107.60  
  Purchase #6 $178.77   10.370%   $197.3084   $197.31   $197.30   $197.30  
  Purchase #7 $70.28   5.397%   $74.073   $74.07   $74.05   $74.10  
  7 purchase totals = $1,011.08       $1,104.5602   $1,104.56   $1,104.55   $1,104.60