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 $46.95   5.783%   $49.6651   $49.67   $49.65   $49.70  
  Purchase #2 $83.54   13.139%   $94.5163   $94.52   $94.50   $94.50  
  Purchase #3 $101.46   6.402%   $107.9555   $107.96   $107.95   $108.00  
  Purchase #4 $224.76   7.391%   $241.372   $241.37   $241.35   $241.40  
  Purchase #5 $91.96   3.866%   $95.5152   $95.52   $95.50   $95.50  
  Purchase #6 $248.70   12.650%   $280.1606   $280.16   $280.15   $280.20  
  Purchase #7 $55.41   4.860%   $58.1029   $58.10   $58.10   $58.10  
  7 purchase totals = $852.78       $927.2876   $927.30   $927.20   $927.40