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 $59.33   6.121%   $62.9616   $62.96   $62.95   $63.00  
  Purchase #2 $107.40   7.394%   $115.3412   $115.34   $115.35   $115.30  
  Purchase #3 $176.63   10.154%   $194.565   $194.57   $194.55   $194.60  
  Purchase #4 $49.79   12.795%   $56.1606   $56.16   $56.15   $56.20  
  Purchase #5 $230.67   12.829%   $260.2627   $260.26   $260.25   $260.30  
  Purchase #6 $158.85   8.427%   $172.2363   $172.24   $172.25   $172.20  
  Purchase #7 $52.77   10.411%   $58.2639   $58.26   $58.25   $58.30  
  7 purchase totals = $835.44       $919.7913   $919.79   $919.75   $919.90