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 $205.75   9.812%   $225.9382   $225.94   $225.95   $225.90  
  Purchase #2 $215.97   6.633%   $230.2953   $230.30   $230.30   $230.30  
  Purchase #3 $202.99   12.210%   $227.7751   $227.78   $227.80   $227.80  
  Purchase #4 $176.66   3.183%   $182.2831   $182.28   $182.30   $182.30  
  Purchase #5 $60.76   6.440%   $64.6729   $64.67   $64.65   $64.70  
  Purchase #6 $223.25   13.865%   $254.2036   $254.20   $254.20   $254.20  
  Purchase #7 $10.77   9.864%   $11.8324   $11.83   $11.85   $11.80  
  7 purchase totals = $1,096.15       $1,197.0006   $1,197.00   $1,197.05   $1,197.00