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 $74.35   3.379%   $76.8623   $76.86   $76.85   $76.90  
  Purchase #2 $134.64   8.827%   $146.5247   $146.52   $146.50   $146.50  
  Purchase #3 $143.58   6.801%   $153.3449   $153.34   $153.35   $153.30  
  Purchase #4 $67.57   8.499%   $73.3128   $73.31   $73.30   $73.30  
  Purchase #5 $116.97   6.233%   $124.2607   $124.26   $124.25   $124.30  
  Purchase #6 $201.38   11.161%   $223.856   $223.86   $223.85   $223.90  
  Purchase #7 $23.39   9.141%   $25.5281   $25.53   $25.55   $25.50  
  7 purchase totals = $761.88       $823.6895   $823.68   $823.65   $823.70