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 $191.66   5.403%   $202.0154   $202.02   $202.00   $202.00  
  Purchase #2 $245.79   10.633%   $271.9249   $271.92   $271.90   $271.90  
  Purchase #3 $154.63   9.763%   $169.7265   $169.73   $169.75   $169.70  
  Purchase #4 $16.63   10.148%   $18.3176   $18.32   $18.30   $18.30  
  Purchase #5 $241.56   11.761%   $269.9699   $269.97   $269.95   $270.00  
  Purchase #6 $127.42   8.541%   $138.3029   $138.30   $138.30   $138.30  
  Purchase #7 $79.30   11.665%   $88.5503   $88.55   $88.55   $88.60  
  7 purchase totals = $1,056.99       $1,158.8075   $1,158.81   $1,158.75   $1,158.80