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 $23.94   3.256%   $24.7195   $24.72   $24.70   $24.70  
  Purchase #2 $155.92   11.555%   $173.9366   $173.94   $173.95   $173.90  
  Purchase #3 $14.55   9.672%   $15.9573   $15.96   $15.95   $16.00  
  Purchase #4 $211.73   10.512%   $233.9871   $233.99   $234.00   $234.00  
  Purchase #5 $187.99   6.499%   $200.2075   $200.21   $200.20   $200.20  
  Purchase #6 $68.75   11.388%   $76.5793   $76.58   $76.60   $76.60  
  Purchase #7 $88.79   7.375%   $95.3383   $95.34   $95.35   $95.30  
  7 purchase totals = $751.67       $820.7256   $820.74   $820.75   $820.70