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 $223.95   7.616%   $241.006   $241.01   $241.00   $241.00  
  Purchase #2 $118.98   13.367%   $134.8841   $134.88   $134.90   $134.90  
  Purchase #3 $190.73   6.352%   $202.8452   $202.85   $202.85   $202.80  
  Purchase #4 $205.65   11.663%   $229.635   $229.64   $229.65   $229.60  
  Purchase #5 $133.39   11.271%   $148.4244   $148.42   $148.40   $148.40  
  Purchase #6 $78.47   5.671%   $82.92   $82.92   $82.90   $82.90  
  Purchase #7 $241.40   10.756%   $267.365   $267.37   $267.35   $267.40  
  7 purchase totals = $1,192.57       $1,307.0797   $1,307.09   $1,307.05   $1,307.00