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 $69.97   5.370%   $73.7274   $73.73   $73.75   $73.70  
  Purchase #2 $118.98   11.494%   $132.6556   $132.66   $132.65   $132.70  
  Purchase #3 $166.75   6.534%   $177.6454   $177.65   $177.65   $177.60  
  Purchase #4 $126.52   5.546%   $133.5368   $133.54   $133.55   $133.50  
  Purchase #5 $194.49   8.746%   $211.5001   $211.50   $211.50   $211.50  
  Purchase #6 $35.60   13.753%   $40.4961   $40.50   $40.50   $40.50  
  Purchase #7 $115.38   11.784%   $128.9764   $128.98   $129.00   $129.00  
  7 purchase totals = $827.69       $898.5378   $898.56   $898.60   $898.50