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 $232.81   13.170%   $263.4711   $263.47   $263.45   $263.50  
  Purchase #2 $99.64   4.858%   $104.4805   $104.48   $104.50   $104.50  
  Purchase #3 $150.43   3.200%   $155.2438   $155.24   $155.25   $155.20  
  Purchase #4 $247.92   7.424%   $266.3256   $266.33   $266.35   $266.30  
  Purchase #5 $197.66   10.685%   $218.78   $218.78   $218.80   $218.80  
  Purchase #6 $146.60   10.343%   $161.7628   $161.76   $161.75   $161.80  
  Purchase #7 $59.37   5.327%   $62.5326   $62.53   $62.55   $62.50  
  7 purchase totals = $1,134.43       $1,232.5964   $1,232.59   $1,232.65   $1,232.60