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 $87.32   12.243%   $98.0106   $98.01   $98.00   $98.00  
  Purchase #2 $215.91   3.636%   $223.7605   $223.76   $223.75   $223.80  
  Purchase #3 $12.40   11.601%   $13.8385   $13.84   $13.85   $13.80  
  Purchase #4 $55.52   4.494%   $58.0151   $58.02   $58.00   $58.00  
  Purchase #5 $85.85   4.185%   $89.4428   $89.44   $89.45   $89.40  
  Purchase #6 $169.65   8.749%   $184.4927   $184.49   $184.50   $184.50  
  Purchase #7 $113.30   11.189%   $125.9771   $125.98   $126.00   $126.00  
  7 purchase totals = $739.95       $793.5373   $793.54   $793.55   $793.50