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 $237.90   8.668%   $258.5212   $258.52   $258.50   $258.50  
  Purchase #2 $232.56   4.204%   $242.3368   $242.34   $242.35   $242.30  
  Purchase #3 $71.36   7.194%   $76.4936   $76.49   $76.50   $76.50  
  Purchase #4 $249.43   4.179%   $259.8537   $259.85   $259.85   $259.90  
  Purchase #5 $172.39   11.617%   $192.4165   $192.42   $192.40   $192.40  
  Purchase #6 $109.70   5.617%   $115.8618   $115.86   $115.85   $115.90  
  Purchase #7 $70.65   13.424%   $80.1341   $80.13   $80.15   $80.10  
  7 purchase totals = $1,143.99       $1,225.6177   $1,225.61   $1,225.60   $1,225.60