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 $121.83   3.242%   $125.7797   $125.78   $125.80   $125.80  
  Purchase #2 $172.72   12.724%   $194.6969   $194.70   $194.70   $194.70  
  Purchase #3 $182.70   10.567%   $202.0059   $202.01   $202.00   $202.00  
  Purchase #4 $198.66   11.313%   $221.1344   $221.13   $221.15   $221.10  
  Purchase #5 $98.81   4.555%   $103.3108   $103.31   $103.30   $103.30  
  Purchase #6 $35.46   5.316%   $37.3451   $37.35   $37.35   $37.30  
  Purchase #7 $201.73   8.862%   $219.6073   $219.61   $219.60   $219.60  
  7 purchase totals = $1,011.91       $1,103.8801   $1,103.89   $1,103.90   $1,103.80