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 $61.78   8.374%   $66.9535   $66.95   $66.95   $67.00  
  Purchase #2 $161.49   7.481%   $173.5711   $173.57   $173.55   $173.60  
  Purchase #3 $34.71   3.865%   $36.0515   $36.05   $36.05   $36.10  
  Purchase #4 $140.26   13.570%   $159.2933   $159.29   $159.30   $159.30  
  Purchase #5 $245.66   8.229%   $265.8754   $265.88   $265.90   $265.90  
  Purchase #6 $85.58   9.105%   $93.3721   $93.37   $93.35   $93.40  
  Purchase #7 $212.96   5.176%   $223.9828   $223.98   $224.00   $224.00  
  7 purchase totals = $942.44       $1,019.0997   $1,019.09   $1,019.10   $1,019.30