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 $46.61   8.752%   $50.6893   $50.69   $50.70   $50.70  
  Purchase #2 $228.38   9.784%   $250.7247   $250.72   $250.70   $250.70  
  Purchase #3 $207.80   11.866%   $232.4575   $232.46   $232.45   $232.50  
  Purchase #4 $246.95   10.814%   $273.6552   $273.66   $273.65   $273.70  
  Purchase #5 $61.66   8.311%   $66.7846   $66.78   $66.80   $66.80  
  Purchase #6 $204.77   10.646%   $226.5698   $226.57   $226.55   $226.60  
  Purchase #7 $160.43   7.422%   $172.3371   $172.34   $172.35   $172.30  
  7 purchase totals = $1,156.60       $1,273.2182   $1,273.22   $1,273.20   $1,273.30