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 $13.68   4.866%   $14.3457   $14.35   $14.35   $14.30  
  Purchase #2 $10.51   8.401%   $11.3929   $11.39   $11.40   $11.40  
  Purchase #3 $45.83   11.606%   $51.149   $51.15   $51.15   $51.10  
  Purchase #4 $116.64   3.745%   $121.0082   $121.01   $121.00   $121.00  
  Purchase #5 $92.78   3.464%   $95.9939   $95.99   $96.00   $96.00  
  Purchase #6 $59.48   8.505%   $64.5388   $64.54   $64.55   $64.50  
  Purchase #7 $64.91   4.275%   $67.6849   $67.68   $67.70   $67.70  
  7 purchase totals = $403.83       $426.1134   $426.11   $426.15   $426.00