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 $235.84   9.114%   $257.3345   $257.33   $257.35   $257.30  
  Purchase #2 $13.83   3.633%   $14.3324   $14.33   $14.35   $14.30  
  Purchase #3 $116.49   8.187%   $126.027   $126.03   $126.05   $126.00  
  Purchase #4 $15.44   6.583%   $16.4564   $16.46   $16.45   $16.50  
  Purchase #5 $103.52   11.211%   $115.1256   $115.13   $115.15   $115.10  
  Purchase #6 $57.40   9.740%   $62.9908   $62.99   $63.00   $63.00  
  Purchase #7 $52.74   13.183%   $59.6927   $59.69   $59.70   $59.70  
  7 purchase totals = $595.26       $651.9594   $651.96   $652.05   $651.90