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 $94.86   10.340%   $104.6685   $104.67   $104.65   $104.70  
  Purchase #2 $96.69   7.844%   $104.2744   $104.27   $104.25   $104.30  
  Purchase #3 $56.98   8.804%   $61.9965   $62.00   $62.00   $62.00  
  Purchase #4 $194.57   3.739%   $201.845   $201.85   $201.85   $201.80  
  Purchase #5 $27.41   11.694%   $30.6153   $30.62   $30.60   $30.60  
  Purchase #6 $142.82   7.228%   $153.143   $153.14   $153.15   $153.10  
  Purchase #7 $140.59   9.184%   $153.5018   $153.50   $153.50   $153.50  
  7 purchase totals = $753.92       $810.0445   $810.05   $810.00   $810.00