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 $118.82   10.303%   $131.062   $131.06   $131.05   $131.10  
  Purchase #2 $72.41   7.538%   $77.8683   $77.87   $77.85   $77.90  
  Purchase #3 $113.48   11.336%   $126.3441   $126.34   $126.35   $126.30  
  Purchase #4 $47.74   3.254%   $49.2935   $49.29   $49.30   $49.30  
  Purchase #5 $191.87   3.145%   $197.9043   $197.90   $197.90   $197.90  
  Purchase #6 $209.53   3.588%   $217.0479   $217.05   $217.05   $217.00  
  Purchase #7 $94.87   3.285%   $97.9865   $97.99   $98.00   $98.00  
  7 purchase totals = $848.72       $897.5066   $897.50   $897.50   $897.50