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 $232.98   11.611%   $260.0313   $260.03   $260.05   $260.00  
  Purchase #2 $199.43   6.126%   $211.6471   $211.65   $211.65   $211.60  
  Purchase #3 $59.77   5.249%   $62.9073   $62.91   $62.90   $62.90  
  Purchase #4 $228.73   6.278%   $243.0897   $243.09   $243.10   $243.10  
  Purchase #5 $233.45   13.217%   $264.3051   $264.31   $264.30   $264.30  
  Purchase #6 $106.34   4.407%   $111.0264   $111.03   $111.05   $111.00  
  Purchase #7 $103.92   12.627%   $117.042   $117.04   $117.05   $117.00  
  7 purchase totals = $1,164.62       $1,270.0489   $1,270.06   $1,270.10   $1,269.90