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 $104.76   12.647%   $118.009   $118.01   $118.00   $118.00  
  Purchase #2 $50.80   8.136%   $54.9331   $54.93   $54.95   $54.90  
  Purchase #3 $105.83   10.210%   $116.6352   $116.64   $116.65   $116.60  
  Purchase #4 $206.46   3.837%   $214.3819   $214.38   $214.40   $214.40  
  Purchase #5 $142.54   4.821%   $149.4119   $149.41   $149.40   $149.40  
  Purchase #6 $105.92   10.467%   $117.0066   $117.01   $117.00   $117.00  
  Purchase #7 $232.49   5.607%   $245.5257   $245.53   $245.55   $245.50  
  7 purchase totals = $948.80       $1,015.9034   $1,015.91   $1,015.95   $1,015.80