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 $209.81   12.246%   $235.5033   $235.50   $235.50   $235.50  
  Purchase #2 $194.42   8.117%   $210.2011   $210.20   $210.20   $210.20  
  Purchase #3 $163.86   8.199%   $177.2949   $177.29   $177.30   $177.30  
  Purchase #4 $100.26   3.517%   $103.7861   $103.79   $103.80   $103.80  
  Purchase #5 $174.78   5.191%   $183.8528   $183.85   $183.85   $183.90  
  Purchase #6 $110.28   11.280%   $122.7196   $122.72   $122.70   $122.70  
  Purchase #7 $211.89   9.494%   $232.0068   $232.01   $232.00   $232.00  
  7 purchase totals = $1,165.30       $1,265.3646   $1,265.36   $1,265.35   $1,265.40