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 $196.93   6.451%   $209.634   $209.63   $209.65   $209.60  
  Purchase #2 $13.64   4.297%   $14.2261   $14.23   $14.25   $14.20  
  Purchase #3 $164.48   3.853%   $170.8174   $170.82   $170.80   $170.80  
  Purchase #4 $60.58   6.252%   $64.3675   $64.37   $64.35   $64.40  
  Purchase #5 $47.70   10.833%   $52.8673   $52.87   $52.85   $52.90  
  Purchase #6 $53.95   13.129%   $61.0331   $61.03   $61.05   $61.00  
  Purchase #7 $211.77   5.309%   $223.0129   $223.01   $223.00   $223.00  
  7 purchase totals = $749.05       $795.9583   $795.96   $795.95   $795.90