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 $242.61   11.217%   $269.8236   $269.82   $269.80   $269.80  
  Purchase #2 $54.69   8.217%   $59.1839   $59.18   $59.20   $59.20  
  Purchase #3 $116.34   5.374%   $122.5921   $122.59   $122.60   $122.60  
  Purchase #4 $79.45   4.344%   $82.9013   $82.90   $82.90   $82.90  
  Purchase #5 $189.71   11.237%   $211.0277   $211.03   $211.05   $211.00  
  Purchase #6 $98.73   11.459%   $110.0435   $110.04   $110.05   $110.00  
  Purchase #7 $186.55   9.410%   $204.1044   $204.10   $204.10   $204.10  
  7 purchase totals = $968.08       $1,059.6765   $1,059.66   $1,059.70   $1,059.60