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 $58.85   6.486%   $62.667   $62.67   $62.65   $62.70  
  Purchase #2 $113.26   11.570%   $126.3642   $126.36   $126.35   $126.40  
  Purchase #3 $60.45   6.174%   $64.1822   $64.18   $64.20   $64.20  
  Purchase #4 $157.36   6.245%   $167.1871   $167.19   $167.20   $167.20  
  Purchase #5 $130.61   5.365%   $137.6172   $137.62   $137.60   $137.60  
  Purchase #6 $41.84   9.702%   $45.8993   $45.90   $45.90   $45.90  
  Purchase #7 $56.60   8.552%   $61.4404   $61.44   $61.45   $61.40  
  7 purchase totals = $618.97       $665.3574   $665.36   $665.35   $665.40