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 $118.28   6.772%   $126.2899   $126.29   $126.30   $126.30  
  Purchase #2 $186.72   10.560%   $206.4376   $206.44   $206.45   $206.40  
  Purchase #3 $177.53   6.759%   $189.5293   $189.53   $189.55   $189.50  
  Purchase #4 $240.86   12.188%   $270.216   $270.22   $270.20   $270.20  
  Purchase #5 $40.96   13.479%   $46.481   $46.48   $46.50   $46.50  
  Purchase #6 $15.33   11.312%   $17.0641   $17.06   $17.05   $17.10  
  Purchase #7 $206.29   10.633%   $228.2248   $228.22   $228.20   $228.20  
  7 purchase totals = $985.97       $1,084.2427   $1,084.24   $1,084.25   $1,084.20