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 $56.83   5.823%   $60.1392   $60.14   $60.15   $60.10  
  Purchase #2 $235.71   6.552%   $251.1537   $251.15   $251.15   $251.20  
  Purchase #3 $243.31   5.121%   $255.7699   $255.77   $255.75   $255.80  
  Purchase #4 $108.30   4.796%   $113.4941   $113.49   $113.50   $113.50  
  Purchase #5 $7.31   12.700%   $8.2384   $8.24   $8.25   $8.20  
  Purchase #6 $191.44   13.431%   $217.1523   $217.15   $217.15   $217.20  
  Purchase #7 $201.84   4.679%   $211.2841   $211.28   $211.30   $211.30  
  7 purchase totals = $1,044.74       $1,117.2317   $1,117.22   $1,117.25   $1,117.30