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 $84.92   8.597%   $92.2206   $92.22   $92.20   $92.20  
  Purchase #2 $205.85   13.371%   $233.3742   $233.37   $233.35   $233.40  
  Purchase #3 $136.62   7.490%   $146.8528   $146.85   $146.85   $146.90  
  Purchase #4 $82.85   3.802%   $86   $86.00   $86.00   $86.00  
  Purchase #5 $149.41   10.111%   $164.5168   $164.52   $164.50   $164.50  
  Purchase #6 $212.59   3.393%   $219.8032   $219.80   $219.80   $219.80  
  Purchase #7 $109.26   5.511%   $115.2813   $115.28   $115.30   $115.30  
  7 purchase totals = $981.50       $1,058.0489   $1,058.04   $1,058.00   $1,058.10