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 $245.53   9.294%   $268.3496   $268.35   $268.35   $268.30  
  Purchase #2 $119.43   9.540%   $130.8236   $130.82   $130.80   $130.80  
  Purchase #3 $88.93   11.650%   $99.2903   $99.29   $99.30   $99.30  
  Purchase #4 $236.83   4.135%   $246.6229   $246.62   $246.60   $246.60  
  Purchase #5 $207.25   8.131%   $224.1015   $224.10   $224.10   $224.10  
  Purchase #6 $54.57   5.397%   $57.5151   $57.52   $57.50   $57.50  
  Purchase #7 $167.49   5.440%   $176.6015   $176.60   $176.60   $176.60  
  7 purchase totals = $1,120.03       $1,203.3045   $1,203.30   $1,203.25   $1,203.20