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 $182.90   10.356%   $201.8411   $201.84   $201.85   $201.80  
  Purchase #2 $225.53   9.716%   $247.4425   $247.44   $247.45   $247.40  
  Purchase #3 $178.94   9.561%   $196.0485   $196.05   $196.05   $196.00  
  Purchase #4 $125.93   5.779%   $133.2075   $133.21   $133.20   $133.20  
  Purchase #5 $180.26   12.198%   $202.2481   $202.25   $202.25   $202.20  
  Purchase #6 $49.57   10.599%   $54.8239   $54.82   $54.80   $54.80  
  Purchase #7 $213.25   6.866%   $227.8917   $227.89   $227.90   $227.90  
  7 purchase totals = $1,156.38       $1,263.5033   $1,263.50   $1,263.50   $1,263.30