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 $46.97   11.442%   $52.3443   $52.34   $52.35   $52.30  
  Purchase #2 $137.29   8.633%   $149.1422   $149.14   $149.15   $149.10  
  Purchase #3 $245.77   7.661%   $264.5984   $264.60   $264.60   $264.60  
  Purchase #4 $196.26   8.797%   $213.525   $213.53   $213.55   $213.50  
  Purchase #5 $221.99   11.375%   $247.2414   $247.24   $247.25   $247.20  
  Purchase #6 $35.28   4.535%   $36.8799   $36.88   $36.90   $36.90  
  Purchase #7 $245.77   13.793%   $279.6691   $279.67   $279.65   $279.70  
  7 purchase totals = $1,129.33       $1,243.4003   $1,243.40   $1,243.45   $1,243.30