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 $245.85   4.762%   $257.5574   $257.56   $257.55   $257.60  
  Purchase #2 $200.75   3.293%   $207.3607   $207.36   $207.35   $207.40  
  Purchase #3 $98.38   6.407%   $104.6832   $104.68   $104.70   $104.70  
  Purchase #4 $108.69   9.525%   $119.0427   $119.04   $119.05   $119.00  
  Purchase #5 $95.34   11.725%   $106.5186   $106.52   $106.50   $106.50  
  Purchase #6 $9.51   5.348%   $10.0186   $10.02   $10.00   $10.00  
  Purchase #7 $88.74   12.119%   $99.4944   $99.49   $99.50   $99.50  
  7 purchase totals = $847.26       $904.6756   $904.67   $904.65   $904.70