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 $227.26   13.462%   $257.8537   $257.85   $257.85   $257.90  
  Purchase #2 $23.94   8.385%   $25.9474   $25.95   $25.95   $25.90  
  Purchase #3 $219.96   12.248%   $246.9007   $246.90   $246.90   $246.90  
  Purchase #4 $12.37   11.304%   $13.7683   $13.77   $13.75   $13.80  
  Purchase #5 $240.27   12.582%   $270.5008   $270.50   $270.50   $270.50  
  Purchase #6 $185.83   7.205%   $199.2191   $199.22   $199.20   $199.20  
  Purchase #7 $95.79   7.196%   $102.683   $102.68   $102.70   $102.70  
  7 purchase totals = $1,005.42       $1,116.8730   $1,116.87   $1,116.85   $1,116.90