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 $208.99   4.783%   $218.986   $218.99   $219.00   $219.00  
  Purchase #2 $118.65   11.254%   $132.0029   $132.00   $132.00   $132.00  
  Purchase #3 $209.36   10.467%   $231.2737   $231.27   $231.25   $231.30  
  Purchase #4 $194.71   4.424%   $203.324   $203.32   $203.30   $203.30  
  Purchase #5 $225.90   12.692%   $254.5712   $254.57   $254.55   $254.60  
  Purchase #6 $5.38   9.851%   $5.91   $5.91   $5.90   $5.90  
  Purchase #7 $241.74   10.437%   $266.9704   $266.97   $266.95   $267.00  
  7 purchase totals = $1,204.73       $1,313.0382   $1,313.03   $1,312.95   $1,313.10