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 $104.78   13.567%   $118.9955   $119.00   $119.00   $119.00  
  Purchase #2 $189.27   12.206%   $212.3723   $212.37   $212.35   $212.40  
  Purchase #3 $184.44   3.817%   $191.4801   $191.48   $191.50   $191.50  
  Purchase #4 $84.75   6.735%   $90.4579   $90.46   $90.45   $90.50  
  Purchase #5 $171.89   3.128%   $177.2667   $177.27   $177.25   $177.30  
  Purchase #6 $156.45   8.826%   $170.2583   $170.26   $170.25   $170.30  
  Purchase #7 $120.34   12.846%   $135.7989   $135.80   $135.80   $135.80  
  7 purchase totals = $1,011.92       $1,096.6297   $1,096.64   $1,096.60   $1,096.80