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 $174.46   13.655%   $198.2825   $198.28   $198.30   $198.30  
  Purchase #2 $60.66   11.227%   $67.4703   $67.47   $67.45   $67.50  
  Purchase #3 $34.80   4.545%   $36.3817   $36.38   $36.40   $36.40  
  Purchase #4 $221.74   7.195%   $237.6942   $237.69   $237.70   $237.70  
  Purchase #5 $220.87   6.592%   $235.4298   $235.43   $235.45   $235.40  
  Purchase #6 $195.97   7.833%   $211.3203   $211.32   $211.30   $211.30  
  Purchase #7 $7.35   7.284%   $7.8854   $7.89   $7.90   $7.90  
  7 purchase totals = $915.85       $994.4642   $994.46   $994.50   $994.50