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 $43.89   9.388%   $48.0104   $48.01   $48.00   $48.00  
  Purchase #2 $56.95   5.303%   $59.9701   $59.97   $59.95   $60.00  
  Purchase #3 $183.68   9.762%   $201.6108   $201.61   $201.60   $201.60  
  Purchase #4 $219.76   3.191%   $226.7725   $226.77   $226.75   $226.80  
  Purchase #5 $20.88   9.755%   $22.9168   $22.92   $22.90   $22.90  
  Purchase #6 $198.27   11.350%   $220.7736   $220.77   $220.75   $220.80  
  Purchase #7 $97.94   5.406%   $103.2346   $103.23   $103.25   $103.20  
  7 purchase totals = $821.37       $883.2888   $883.28   $883.20   $883.30