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 $147.95   9.599%   $162.1517   $162.15   $162.15   $162.20  
  Purchase #2 $244.39   4.262%   $254.8059   $254.81   $254.80   $254.80  
  Purchase #3 $67.88   5.686%   $71.7397   $71.74   $71.75   $71.70  
  Purchase #4 $211.51   6.320%   $224.8774   $224.88   $224.90   $224.90  
  Purchase #5 $152.78   11.148%   $169.8119   $169.81   $169.80   $169.80  
  Purchase #6 $97.32   4.310%   $101.5145   $101.51   $101.50   $101.50  
  Purchase #7 $248.85   3.568%   $257.729   $257.73   $257.75   $257.70  
  7 purchase totals = $1,170.68       $1,242.6301   $1,242.63   $1,242.65   $1,242.60