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 $196.47   6.664%   $209.5628   $209.56   $209.55   $209.60  
  Purchase #2 $126.93   7.417%   $136.3444   $136.34   $136.35   $136.30  
  Purchase #3 $186.93   9.561%   $204.8024   $204.80   $204.80   $204.80  
  Purchase #4 $218.61   9.247%   $238.8249   $238.82   $238.80   $238.80  
  Purchase #5 $154.42   3.506%   $159.834   $159.83   $159.85   $159.80  
  Purchase #6 $33.45   10.530%   $36.9723   $36.97   $36.95   $37.00  
  Purchase #7 $45.61   7.182%   $48.8857   $48.89   $48.90   $48.90  
  7 purchase totals = $962.42       $1,035.2265   $1,035.21   $1,035.20   $1,035.20