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 $82.62   12.754%   $93.1574   $93.16   $93.15   $93.20  
  Purchase #2 $243.27   7.738%   $262.0942   $262.09   $262.10   $262.10  
  Purchase #3 $49.45   5.717%   $52.2771   $52.28   $52.30   $52.30  
  Purchase #4 $195.59   4.446%   $204.2859   $204.29   $204.30   $204.30  
  Purchase #5 $58.50   9.279%   $63.9282   $63.93   $63.95   $63.90  
  Purchase #6 $177.75   7.621%   $191.2963   $191.30   $191.30   $191.30  
  Purchase #7 $209.89   10.342%   $231.5968   $231.60   $231.60   $231.60  
  7 purchase totals = $1,017.07       $1,098.6359   $1,098.65   $1,098.70   $1,098.70