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 $190.74   6.467%   $203.0752   $203.08   $203.10   $203.10  
  Purchase #2 $63.92   11.813%   $71.4709   $71.47   $71.45   $71.50  
  Purchase #3 $247.30   11.743%   $276.3404   $276.34   $276.35   $276.30  
  Purchase #4 $230.84   9.378%   $252.4882   $252.49   $252.50   $252.50  
  Purchase #5 $218.78   6.806%   $233.6702   $233.67   $233.65   $233.70  
  Purchase #6 $119.61   5.324%   $125.978   $125.98   $126.00   $126.00  
  Purchase #7 $82.47   12.634%   $92.8893   $92.89   $92.90   $92.90  
  7 purchase totals = $1,153.66       $1,255.9122   $1,255.92   $1,255.95   $1,256.00