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 $235.45   13.638%   $267.5607   $267.56   $267.55   $267.60  
  Purchase #2 $55.71   11.305%   $62.008   $62.01   $62.00   $62.00  
  Purchase #3 $182.57   12.364%   $205.143   $205.14   $205.15   $205.10  
  Purchase #4 $9.36   13.300%   $10.6049   $10.60   $10.60   $10.60  
  Purchase #5 $169.93   8.279%   $183.9985   $184.00   $184.00   $184.00  
  Purchase #6 $244.93   5.249%   $257.7864   $257.79   $257.80   $257.80  
  Purchase #7 $166.53   10.737%   $184.4103   $184.41   $184.40   $184.40  
  7 purchase totals = $1,064.48       $1,171.5118   $1,171.51   $1,171.50   $1,171.50