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 $196.34   4.277%   $204.7375   $204.74   $204.75   $204.70  
  Purchase #2 $211.27   7.780%   $227.7068   $227.71   $227.70   $227.70  
  Purchase #3 $87.96   6.773%   $93.9175   $93.92   $93.90   $93.90  
  Purchase #4 $5.96   10.485%   $6.5849   $6.58   $6.60   $6.60  
  Purchase #5 $168.79   4.115%   $175.7357   $175.74   $175.75   $175.70  
  Purchase #6 $99.86   13.253%   $113.0944   $113.09   $113.10   $113.10  
  Purchase #7 $171.78   13.555%   $195.0648   $195.06   $195.05   $195.10  
  7 purchase totals = $941.96       $1,016.8416   $1,016.84   $1,016.85   $1,016.80