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 $66.52   12.809%   $75.0405   $75.04   $75.05   $75.00  
  Purchase #2 $166.31   6.661%   $177.3879   $177.39   $177.40   $177.40  
  Purchase #3 $164.95   7.803%   $177.821   $177.82   $177.80   $177.80  
  Purchase #4 $101.87   6.692%   $108.6871   $108.69   $108.70   $108.70  
  Purchase #5 $75.70   7.873%   $81.6599   $81.66   $81.65   $81.70  
  Purchase #6 $69.35   6.345%   $73.7503   $73.75   $73.75   $73.80  
  Purchase #7 $209.35   13.134%   $236.846   $236.85   $236.85   $236.80  
  7 purchase totals = $854.05       $931.1927   $931.20   $931.20   $931.20