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 $82.69   12.720%   $93.2082   $93.21   $93.20   $93.20  
  Purchase #2 $172.64   13.464%   $195.8842   $195.88   $195.90   $195.90  
  Purchase #3 $210.86   11.299%   $234.6851   $234.69   $234.70   $234.70  
  Purchase #4 $63.31   4.874%   $66.3957   $66.40   $66.40   $66.40  
  Purchase #5 $69.57   13.460%   $78.9341   $78.93   $78.95   $78.90  
  Purchase #6 $203.62   5.420%   $214.6562   $214.66   $214.65   $214.70  
  Purchase #7 $190.79   7.289%   $204.6967   $204.70   $204.70   $204.70  
  7 purchase totals = $993.48       $1,088.4602   $1,088.47   $1,088.50   $1,088.50