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 $234.63   8.569%   $254.7354   $254.74   $254.75   $254.70  
  Purchase #2 $179.39   13.628%   $203.8373   $203.84   $203.85   $203.80  
  Purchase #3 $226.64   10.368%   $250.138   $250.14   $250.15   $250.10  
  Purchase #4 $97.44   12.153%   $109.2819   $109.28   $109.30   $109.30  
  Purchase #5 $165.35   5.810%   $174.9568   $174.96   $174.95   $175.00  
  Purchase #6 $117.34   3.511%   $121.4598   $121.46   $121.45   $121.50  
  Purchase #7 $71.67   6.289%   $76.1773   $76.18   $76.20   $76.20  
  7 purchase totals = $1,092.46       $1,190.5865   $1,190.60   $1,190.65   $1,190.60