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 $85.38   8.778%   $92.8747   $92.87   $92.85   $92.90  
  Purchase #2 $169.87   5.826%   $179.7666   $179.77   $179.75   $179.80  
  Purchase #3 $27.72   5.721%   $29.3059   $29.31   $29.30   $29.30  
  Purchase #4 $52.62   6.456%   $56.0171   $56.02   $56.00   $56.00  
  Purchase #5 $96.29   5.539%   $101.6235   $101.62   $101.60   $101.60  
  Purchase #6 $226.37   5.120%   $237.9601   $237.96   $237.95   $238.00  
  Purchase #7 $120.61   3.867%   $125.274   $125.27   $125.25   $125.30  
  7 purchase totals = $778.86       $822.8219   $822.82   $822.70   $822.90