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 $60.27   7.351%   $64.7004   $64.70   $64.70   $64.70  
  Purchase #2 $89.35   4.782%   $93.6227   $93.62   $93.60   $93.60  
  Purchase #3 $146.49   7.183%   $157.0124   $157.01   $157.00   $157.00  
  Purchase #4 $29.33   9.180%   $32.0225   $32.02   $32.00   $32.00  
  Purchase #5 $34.40   10.156%   $37.8937   $37.89   $37.90   $37.90  
  Purchase #6 $239.89   11.673%   $267.8924   $267.89   $267.90   $267.90  
  Purchase #7 $159.44   8.797%   $173.4659   $173.47   $173.45   $173.50  
  7 purchase totals = $759.17       $826.6100   $826.60   $826.55   $826.60