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 $54.37   10.735%   $60.2066   $60.21   $60.20   $60.20  
  Purchase #2 $157.98   12.421%   $177.6027   $177.60   $177.60   $177.60  
  Purchase #3 $210.98   10.346%   $232.808   $232.81   $232.80   $232.80  
  Purchase #4 $63.36   9.453%   $69.3494   $69.35   $69.35   $69.30  
  Purchase #5 $153.31   7.656%   $165.0474   $165.05   $165.05   $165.00  
  Purchase #6 $238.81   6.397%   $254.0867   $254.09   $254.10   $254.10  
  Purchase #7 $248.32   9.829%   $272.7274   $272.73   $272.75   $272.70  
  7 purchase totals = $1,127.13       $1,231.8282   $1,231.84   $1,231.85   $1,231.70