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 $66.50   13.541%   $75.5048   $75.50   $75.50   $75.50  
  Purchase #2 $157.73   11.796%   $176.3358   $176.34   $176.35   $176.30  
  Purchase #3 $168.57   5.498%   $177.838   $177.84   $177.85   $177.80  
  Purchase #4 $97.52   3.810%   $101.2355   $101.24   $101.25   $101.20  
  Purchase #5 $234.98   12.603%   $264.5945   $264.59   $264.60   $264.60  
  Purchase #6 $129.70   8.354%   $140.5351   $140.54   $140.55   $140.50  
  Purchase #7 $13.35   10.374%   $14.7349   $14.73   $14.75   $14.70  
  7 purchase totals = $868.35       $950.7786   $950.78   $950.85   $950.60