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 $182.54   6.815%   $194.9801   $194.98   $195.00   $195.00  
  Purchase #2 $250.45   9.628%   $274.5633   $274.56   $274.55   $274.60  
  Purchase #3 $16.66   6.111%   $17.6781   $17.68   $17.70   $17.70  
  Purchase #4 $193.69   8.297%   $209.7605   $209.76   $209.75   $209.80  
  Purchase #5 $230.72   9.814%   $253.3629   $253.36   $253.35   $253.40  
  Purchase #6 $65.55   9.797%   $71.9719   $71.97   $71.95   $72.00  
  Purchase #7 $13.38   12.869%   $15.1019   $15.10   $15.10   $15.10  
  7 purchase totals = $952.99       $1,037.4187   $1,037.41   $1,037.40   $1,037.60