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 $150.92   10.716%   $167.0926   $167.09   $167.10   $167.10  
  Purchase #2 $13.50   8.399%   $14.6339   $14.63   $14.65   $14.60  
  Purchase #3 $53.70   5.779%   $56.8033   $56.80   $56.80   $56.80  
  Purchase #4 $190.93   3.310%   $197.2498   $197.25   $197.25   $197.20  
  Purchase #5 $49.75   12.179%   $55.8091   $55.81   $55.80   $55.80  
  Purchase #6 $169.84   11.444%   $189.2765   $189.28   $189.30   $189.30  
  Purchase #7 $72.62   5.307%   $76.4739   $76.47   $76.45   $76.50  
  7 purchase totals = $701.26       $757.3391   $757.33   $757.35   $757.30