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 $84.66   10.623%   $93.6534   $93.65   $93.65   $93.70  
  Purchase #2 $147.96   12.311%   $166.1754   $166.18   $166.20   $166.20  
  Purchase #3 $87.33   7.328%   $93.7295   $93.73   $93.75   $93.70  
  Purchase #4 $220.51   13.207%   $249.6328   $249.63   $249.65   $249.60  
  Purchase #5 $25.45   13.463%   $28.8763   $28.88   $28.90   $28.90  
  Purchase #6 $229.38   4.617%   $239.9705   $239.97   $239.95   $240.00  
  Purchase #7 $186.79   12.679%   $210.4731   $210.47   $210.45   $210.50  
  7 purchase totals = $982.08       $1,082.5110   $1,082.51   $1,082.55   $1,082.60