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 $234.84   10.106%   $258.5729   $258.57   $258.55   $258.60  
  Purchase #2 $60.46   3.626%   $62.6523   $62.65   $62.65   $62.70  
  Purchase #3 $58.26   4.400%   $60.8234   $60.82   $60.80   $60.80  
  Purchase #4 $242.44   13.608%   $275.4312   $275.43   $275.45   $275.40  
  Purchase #5 $223.90   12.200%   $251.2158   $251.22   $251.20   $251.20  
  Purchase #6 $128.74   6.513%   $137.1248   $137.12   $137.10   $137.10  
  Purchase #7 $152.49   3.515%   $157.85   $157.85   $157.85   $157.90  
  7 purchase totals = $1,101.13       $1,203.6704   $1,203.66   $1,203.60   $1,203.70