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 $82.53   11.458%   $91.9863   $91.99   $92.00   $92.00  
  Purchase #2 $162.90   4.561%   $170.3299   $170.33   $170.35   $170.30  
  Purchase #3 $119.77   10.686%   $132.5686   $132.57   $132.55   $132.60  
  Purchase #4 $84.95   4.839%   $89.0607   $89.06   $89.05   $89.10  
  Purchase #5 $52.94   6.805%   $56.5426   $56.54   $56.55   $56.50  
  Purchase #6 $79.27   3.450%   $82.0048   $82.00   $82.00   $82.00  
  Purchase #7 $97.26   13.504%   $110.394   $110.39   $110.40   $110.40  
  7 purchase totals = $679.62       $732.8869   $732.88   $732.90   $732.90