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 $242.52   11.180%   $269.6337   $269.63   $269.65   $269.60  
  Purchase #2 $156.54   6.496%   $166.7088   $166.71   $166.70   $166.70  
  Purchase #3 $108.93   3.494%   $112.736   $112.74   $112.75   $112.70  
  Purchase #4 $177.33   11.211%   $197.2105   $197.21   $197.20   $197.20  
  Purchase #5 $207.58   5.645%   $219.2979   $219.30   $219.30   $219.30  
  Purchase #6 $194.35   7.681%   $209.278   $209.28   $209.30   $209.30  
  Purchase #7 $28.56   10.212%   $31.4765   $31.48   $31.50   $31.50  
  7 purchase totals = $1,115.81       $1,206.3414   $1,206.35   $1,206.40   $1,206.30