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 $234.89   12.828%   $265.0217   $265.02   $265.00   $265.00  
  Purchase #2 $185.77   9.271%   $202.9927   $202.99   $203.00   $203.00  
  Purchase #3 $138.46   13.839%   $157.6215   $157.62   $157.60   $157.60  
  Purchase #4 $229.65   10.596%   $253.9837   $253.98   $254.00   $254.00  
  Purchase #5 $83.31   5.646%   $88.0137   $88.01   $88.00   $88.00  
  Purchase #6 $185.91   3.459%   $192.3406   $192.34   $192.35   $192.30  
  Purchase #7 $38.74   10.615%   $42.8523   $42.85   $42.85   $42.90  
  7 purchase totals = $1,096.73       $1,202.8262   $1,202.81   $1,202.80   $1,202.80