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 $198.76   3.144%   $205.009   $205.01   $205.00   $205.00  
  Purchase #2 $34.65   5.670%   $36.6147   $36.61   $36.60   $36.60  
  Purchase #3 $148.86   8.331%   $161.2615   $161.26   $161.25   $161.30  
  Purchase #4 $61.67   3.210%   $63.6496   $63.65   $63.65   $63.60  
  Purchase #5 $226.84   4.605%   $237.286   $237.29   $237.30   $237.30  
  Purchase #6 $230.71   6.440%   $245.5677   $245.57   $245.55   $245.60  
  Purchase #7 $133.70   8.299%   $144.7958   $144.80   $144.80   $144.80  
  7 purchase totals = $1,035.19       $1,094.1843   $1,094.19   $1,094.15   $1,094.20