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 $88.45   6.423%   $94.1311   $94.13   $94.15   $94.10  
  Purchase #2 $122.33   3.421%   $126.5149   $126.51   $126.50   $126.50  
  Purchase #3 $187.98   9.622%   $206.0674   $206.07   $206.05   $206.10  
  Purchase #4 $46.67   6.327%   $49.6228   $49.62   $49.60   $49.60  
  Purchase #5 $203.35   7.112%   $217.8123   $217.81   $217.80   $217.80  
  Purchase #6 $175.43   9.830%   $192.6748   $192.67   $192.65   $192.70  
  Purchase #7 $44.77   11.322%   $49.8389   $49.84   $49.85   $49.80  
  7 purchase totals = $868.98       $936.6622   $936.65   $936.60   $936.60