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 $57.94   5.642%   $61.209   $61.21   $61.20   $61.20  
  Purchase #2 $87.53   9.541%   $95.8812   $95.88   $95.90   $95.90  
  Purchase #3 $84.30   8.585%   $91.5372   $91.54   $91.55   $91.50  
  Purchase #4 $223.28   9.797%   $245.1547   $245.15   $245.15   $245.20  
  Purchase #5 $144.50   3.756%   $149.9274   $149.93   $149.95   $149.90  
  Purchase #6 $108.67   9.734%   $119.2479   $119.25   $119.25   $119.20  
  Purchase #7 $238.60   13.448%   $270.6869   $270.69   $270.70   $270.70  
  7 purchase totals = $944.82       $1,033.6443   $1,033.65   $1,033.70   $1,033.60