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 $58.37   7.343%   $62.6561   $62.66   $62.65   $62.70  
  Purchase #2 $225.25   10.571%   $249.0612   $249.06   $249.05   $249.10  
  Purchase #3 $227.46   10.380%   $251.0703   $251.07   $251.05   $251.10  
  Purchase #4 $29.55   12.122%   $33.1321   $33.13   $33.15   $33.10  
  Purchase #5 $68.82   6.844%   $73.53   $73.53   $73.55   $73.50  
  Purchase #6 $151.75   3.576%   $157.1766   $157.18   $157.20   $157.20  
  Purchase #7 $199.97   6.682%   $213.332   $213.33   $213.35   $213.30  
  7 purchase totals = $961.17       $1,039.9583   $1,039.96   $1,040.00   $1,040.00