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 $168.84   9.741%   $185.2867   $185.29   $185.30   $185.30  
  Purchase #2 $235.86   13.612%   $267.9653   $267.97   $267.95   $268.00  
  Purchase #3 $65.58   7.293%   $70.3627   $70.36   $70.35   $70.40  
  Purchase #4 $108.53   3.238%   $112.0442   $112.04   $112.05   $112.00  
  Purchase #5 $87.35   9.689%   $95.8133   $95.81   $95.80   $95.80  
  Purchase #6 $108.32   11.269%   $120.5266   $120.53   $120.55   $120.50  
  Purchase #7 $206.87   12.581%   $232.8963   $232.90   $232.90   $232.90  
  7 purchase totals = $981.35       $1,084.8951   $1,084.90   $1,084.90   $1,084.90