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 $57.98   5.260%   $61.0297   $61.03   $61.05   $61.00  
  Purchase #2 $168.46   5.214%   $177.2435   $177.24   $177.25   $177.20  
  Purchase #3 $113.46   12.188%   $127.2885   $127.29   $127.30   $127.30  
  Purchase #4 $34.52   4.183%   $35.964   $35.96   $35.95   $36.00  
  Purchase #5 $249.26   6.144%   $264.5745   $264.57   $264.55   $264.60  
  Purchase #6 $73.69   7.476%   $79.1991   $79.20   $79.20   $79.20  
  Purchase #7 $42.40   10.459%   $46.8346   $46.83   $46.85   $46.80  
  7 purchase totals = $739.77       $792.1339   $792.12   $792.15   $792.10