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 $236.93   12.824%   $267.3139   $267.31   $267.30   $267.30  
  Purchase #2 $153.99   4.650%   $161.1505   $161.15   $161.15   $161.20  
  Purchase #3 $176.78   13.507%   $200.6577   $200.66   $200.65   $200.70  
  Purchase #4 $186.92   8.165%   $202.182   $202.18   $202.20   $202.20  
  Purchase #5 $247.55   8.362%   $268.2501   $268.25   $268.25   $268.30  
  Purchase #6 $232.72   4.437%   $243.0458   $243.05   $243.05   $243.00  
  Purchase #7 $21.89   7.707%   $23.5771   $23.58   $23.60   $23.60  
  7 purchase totals = $1,256.78       $1,366.1771   $1,366.18   $1,366.20   $1,366.30