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 $161.42   3.432%   $166.9599   $166.96   $166.95   $167.00  
  Purchase #2 $13.39   5.395%   $14.1124   $14.11   $14.10   $14.10  
  Purchase #3 $229.61   4.616%   $240.2088   $240.21   $240.20   $240.20  
  Purchase #4 $68.27   3.153%   $70.4226   $70.42   $70.40   $70.40  
  Purchase #5 $104.56   3.781%   $108.5134   $108.51   $108.50   $108.50  
  Purchase #6 $114.67   9.141%   $125.152   $125.15   $125.15   $125.20  
  Purchase #7 $240.32   6.319%   $255.5058   $255.51   $255.50   $255.50  
  7 purchase totals = $932.24       $980.8749   $980.87   $980.80   $980.90