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 $8.50   10.133%   $9.3613   $9.36   $9.35   $9.40  
  Purchase #2 $54.89   7.641%   $59.0841   $59.08   $59.10   $59.10  
  Purchase #3 $107.89   12.829%   $121.7312   $121.73   $121.75   $121.70  
  Purchase #4 $48.73   9.162%   $53.1946   $53.19   $53.20   $53.20  
  Purchase #5 $70.44   12.359%   $79.1457   $79.15   $79.15   $79.10  
  Purchase #6 $146.68   3.485%   $151.7918   $151.79   $151.80   $151.80  
  Purchase #7 $92.48   12.359%   $103.9096   $103.91   $103.90   $103.90  
  7 purchase totals = $529.61       $578.2183   $578.21   $578.25   $578.20