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 $84.71   10.827%   $93.8816   $93.88   $93.90   $93.90  
  Purchase #2 $60.50   5.428%   $63.7839   $63.78   $63.80   $63.80  
  Purchase #3 $181.29   6.308%   $192.7258   $192.73   $192.75   $192.70  
  Purchase #4 $240.88   4.829%   $252.5121   $252.51   $252.50   $252.50  
  Purchase #5 $34.71   4.570%   $36.2962   $36.30   $36.30   $36.30  
  Purchase #6 $158.38   5.588%   $167.2303   $167.23   $167.25   $167.20  
  Purchase #7 $187.77   3.770%   $194.8489   $194.85   $194.85   $194.80  
  7 purchase totals = $948.24       $1,001.2788   $1,001.28   $1,001.35   $1,001.20