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 $58.92   10.819%   $65.2946   $65.29   $65.30   $65.30  
  Purchase #2 $26.97   5.692%   $28.5051   $28.51   $28.50   $28.50  
  Purchase #3 $132.26   13.447%   $150.045   $150.05   $150.05   $150.00  
  Purchase #4 $72.85   13.505%   $82.6884   $82.69   $82.70   $82.70  
  Purchase #5 $21.66   10.834%   $24.0066   $24.01   $24.00   $24.00  
  Purchase #6 $34.39   6.367%   $36.5796   $36.58   $36.60   $36.60  
  Purchase #7 $222.47   11.337%   $247.6914   $247.69   $247.70   $247.70  
  7 purchase totals = $569.52       $634.8107   $634.82   $634.85   $634.80