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 $60.92   5.528%   $64.2877   $64.29   $64.30   $64.30  
  Purchase #2 $226.77   9.253%   $247.753   $247.75   $247.75   $247.80  
  Purchase #3 $83.67   5.203%   $88.0234   $88.02   $88.00   $88.00  
  Purchase #4 $94.87   12.844%   $107.0551   $107.06   $107.05   $107.10  
  Purchase #5 $140.83   5.582%   $148.6911   $148.69   $148.70   $148.70  
  Purchase #6 $187.94   10.416%   $207.5158   $207.52   $207.50   $207.50  
  Purchase #7 $102.93   9.271%   $112.4726   $112.47   $112.45   $112.50  
  7 purchase totals = $897.93       $975.7987   $975.80   $975.75   $975.90