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 $64.48   5.549%   $68.058   $68.06   $68.05   $68.10  
  Purchase #2 $82.85   10.790%   $91.7895   $91.79   $91.80   $91.80  
  Purchase #3 $31.47   6.665%   $33.5675   $33.57   $33.55   $33.60  
  Purchase #4 $151.45   10.386%   $167.1796   $167.18   $167.20   $167.20  
  Purchase #5 $87.26   4.788%   $91.438   $91.44   $91.45   $91.40  
  Purchase #6 $235.46   9.675%   $258.2408   $258.24   $258.25   $258.20  
  Purchase #7 $15.41   12.138%   $17.2805   $17.28   $17.30   $17.30  
  7 purchase totals = $668.38       $727.5539   $727.56   $727.60   $727.60