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 $242.39   11.373%   $269.957   $269.96   $269.95   $270.00  
  Purchase #2 $111.84   5.147%   $117.5964   $117.60   $117.60   $117.60  
  Purchase #3 $124.85   8.218%   $135.1102   $135.11   $135.10   $135.10  
  Purchase #4 $216.97   5.418%   $228.7254   $228.73   $228.75   $228.70  
  Purchase #5 $233.71   9.427%   $255.7418   $255.74   $255.75   $255.70  
  Purchase #6 $189.74   8.520%   $205.9058   $205.91   $205.90   $205.90  
  Purchase #7 $182.26   8.798%   $198.2952   $198.30   $198.30   $198.30  
  7 purchase totals = $1,301.76       $1,411.3318   $1,411.35   $1,411.35   $1,411.30