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 $216.52   12.761%   $244.1501   $244.15   $244.15   $244.20  
  Purchase #2 $197.99   12.228%   $222.2002   $222.20   $222.20   $222.20  
  Purchase #3 $166.46   12.840%   $187.8335   $187.83   $187.85   $187.80  
  Purchase #4 $102.66   5.113%   $107.909   $107.91   $107.90   $107.90  
  Purchase #5 $189.51   5.129%   $199.23   $199.23   $199.25   $199.20  
  Purchase #6 $128.51   12.355%   $144.3874   $144.39   $144.40   $144.40  
  Purchase #7 $244.96   5.246%   $257.8106   $257.81   $257.80   $257.80  
  7 purchase totals = $1,246.61       $1,363.5208   $1,363.52   $1,363.55   $1,363.50