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 $210.53   10.462%   $232.5556   $232.56   $232.55   $232.60  
  Purchase #2 $120.39   12.368%   $135.2798   $135.28   $135.30   $135.30  
  Purchase #3 $103.92   7.597%   $111.8148   $111.81   $111.80   $111.80  
  Purchase #4 $230.33   3.687%   $238.8223   $238.82   $238.80   $238.80  
  Purchase #5 $32.50   3.474%   $33.6291   $33.63   $33.65   $33.60  
  Purchase #6 $93.31   10.642%   $103.2401   $103.24   $103.25   $103.20  
  Purchase #7 $17.76   12.774%   $20.0287   $20.03   $20.05   $20.00  
  7 purchase totals = $808.74       $875.3704   $875.37   $875.40   $875.30