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 $95.81   7.438%   $102.9363   $102.94   $102.95   $102.90  
  Purchase #2 $169.72   4.557%   $177.4541   $177.45   $177.45   $177.50  
  Purchase #3 $53.33   12.796%   $60.1541   $60.15   $60.15   $60.20  
  Purchase #4 $222.44   12.322%   $249.8491   $249.85   $249.85   $249.80  
  Purchase #5 $10.73   5.628%   $11.3339   $11.33   $11.35   $11.30  
  Purchase #6 $204.91   10.397%   $226.2145   $226.21   $226.20   $226.20  
  Purchase #7 $170.88   8.486%   $185.3809   $185.38   $185.40   $185.40  
  7 purchase totals = $927.82       $1,013.3229   $1,013.31   $1,013.35   $1,013.30