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 $202.87   10.515%   $224.2018   $224.20   $224.20   $224.20  
  Purchase #2 $60.94   12.543%   $68.5837   $68.58   $68.60   $68.60  
  Purchase #3 $76.37   5.705%   $80.7269   $80.73   $80.75   $80.70  
  Purchase #4 $161.89   3.298%   $167.2291   $167.23   $167.25   $167.20  
  Purchase #5 $185.35   9.282%   $202.5542   $202.55   $202.55   $202.60  
  Purchase #6 $218.92   11.853%   $244.8686   $244.87   $244.85   $244.90  
  Purchase #7 $178.97   4.772%   $187.5104   $187.51   $187.50   $187.50  
  7 purchase totals = $1,085.31       $1,175.6747   $1,175.67   $1,175.70   $1,175.70