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 $182.52   11.140%   $202.8527   $202.85   $202.85   $202.90  
  Purchase #2 $24.74   12.240%   $27.7682   $27.77   $27.75   $27.80  
  Purchase #3 $107.37   3.139%   $110.7403   $110.74   $110.75   $110.70  
  Purchase #4 $241.37   10.511%   $266.7404   $266.74   $266.75   $266.70  
  Purchase #5 $121.47   12.415%   $136.5505   $136.55   $136.55   $136.60  
  Purchase #6 $86.56   11.251%   $96.2989   $96.30   $96.30   $96.30  
  Purchase #7 $63.76   4.129%   $66.3927   $66.39   $66.40   $66.40  
  7 purchase totals = $827.79       $907.3437   $907.34   $907.35   $907.40