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 $185.46   11.468%   $206.7286   $206.73   $206.75   $206.70  
  Purchase #2 $247.36   10.329%   $272.9098   $272.91   $272.90   $272.90  
  Purchase #3 $71.78   6.596%   $76.5146   $76.51   $76.50   $76.50  
  Purchase #4 $136.96   13.460%   $155.3948   $155.39   $155.40   $155.40  
  Purchase #5 $80.93   6.520%   $86.2066   $86.21   $86.20   $86.20  
  Purchase #6 $101.94   8.470%   $110.5743   $110.57   $110.55   $110.60  
  Purchase #7 $217.56   11.235%   $242.0029   $242.00   $242.00   $242.00  
  7 purchase totals = $1,041.99       $1,150.3316   $1,150.32   $1,150.30   $1,150.30