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 $203.80   3.141%   $210.2014   $210.20   $210.20   $210.20  
  Purchase #2 $227.38   3.651%   $235.6816   $235.68   $235.70   $235.70  
  Purchase #3 $76.35   3.616%   $79.1108   $79.11   $79.10   $79.10  
  Purchase #4 $157.51   5.743%   $166.5558   $166.56   $166.55   $166.60  
  Purchase #5 $118.60   9.412%   $129.7626   $129.76   $129.75   $129.80  
  Purchase #6 $31.84   9.407%   $34.8352   $34.84   $34.85   $34.80  
  Purchase #7 $61.66   12.689%   $69.484   $69.48   $69.50   $69.50  
  7 purchase totals = $877.14       $925.6314   $925.63   $925.65   $925.70