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 $65.85   11.571%   $73.4695   $73.47   $73.45   $73.50  
  Purchase #2 $5.49   3.506%   $5.6825   $5.68   $5.70   $5.70  
  Purchase #3 $175.77   4.561%   $183.7869   $183.79   $183.80   $183.80  
  Purchase #4 $33.34   4.597%   $34.8726   $34.87   $34.85   $34.90  
  Purchase #5 $146.54   4.745%   $153.4933   $153.49   $153.50   $153.50  
  Purchase #6 $190.55   10.279%   $210.1366   $210.14   $210.15   $210.10  
  Purchase #7 $176.89   8.834%   $192.5165   $192.52   $192.50   $192.50  
  7 purchase totals = $794.43       $853.9579   $853.96   $853.95   $854.00