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 $61.78   6.511%   $65.8025   $65.80   $65.80   $65.80  
  Purchase #2 $108.83   4.146%   $113.3421   $113.34   $113.35   $113.30  
  Purchase #3 $228.75   7.678%   $246.3134   $246.31   $246.30   $246.30  
  Purchase #4 $210.65   3.393%   $217.7974   $217.80   $217.80   $217.80  
  Purchase #5 $208.83   3.855%   $216.8804   $216.88   $216.90   $216.90  
  Purchase #6 $232.84   12.421%   $261.7611   $261.76   $261.75   $261.80  
  Purchase #7 $216.68   4.476%   $226.3786   $226.38   $226.40   $226.40  
  7 purchase totals = $1,268.36       $1,348.2755   $1,348.27   $1,348.30   $1,348.30