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 $206.52   13.810%   $235.0404   $235.04   $235.05   $235.00  
  Purchase #2 $126.92   5.445%   $133.8308   $133.83   $133.85   $133.80  
  Purchase #3 $205.56   3.732%   $213.2315   $213.23   $213.25   $213.20  
  Purchase #4 $202.85   10.226%   $223.5934   $223.59   $223.60   $223.60  
  Purchase #5 $190.94   10.584%   $211.1491   $211.15   $211.15   $211.10  
  Purchase #6 $250.56   6.412%   $266.6259   $266.63   $266.65   $266.60  
  Purchase #7 $210.62   5.323%   $221.8313   $221.83   $221.85   $221.80  
  7 purchase totals = $1,393.97       $1,505.3024   $1,505.30   $1,505.40   $1,505.10