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 $60.98   7.567%   $65.5944   $65.59   $65.60   $65.60  
  Purchase #2 $245.51   5.499%   $259.0106   $259.01   $259.00   $259.00  
  Purchase #3 $27.58   6.129%   $29.2704   $29.27   $29.25   $29.30  
  Purchase #4 $102.46   10.365%   $113.08   $113.08   $113.10   $113.10  
  Purchase #5 $175.41   11.294%   $195.2208   $195.22   $195.20   $195.20  
  Purchase #6 $54.42   3.441%   $56.2926   $56.29   $56.30   $56.30  
  Purchase #7 $111.48   12.624%   $125.5532   $125.55   $125.55   $125.60  
  7 purchase totals = $777.84       $844.0220   $844.01   $844.00   $844.10