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 $66.82   10.308%   $73.7078   $73.71   $73.70   $73.70  
  Purchase #2 $210.98   13.757%   $240.0045   $240.00   $240.00   $240.00  
  Purchase #3 $66.52   13.734%   $75.6559   $75.66   $75.65   $75.70  
  Purchase #4 $5.29   5.751%   $5.5942   $5.59   $5.60   $5.60  
  Purchase #5 $216.75   10.229%   $238.9214   $238.92   $238.90   $238.90  
  Purchase #6 $23.88   11.543%   $26.6365   $26.64   $26.65   $26.60  
  Purchase #7 $176.51   10.322%   $194.7294   $194.73   $194.75   $194.70  
  7 purchase totals = $766.75       $855.2497   $855.25   $855.25   $855.20