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 $61.83   12.132%   $69.3312   $69.33   $69.35   $69.30  
  Purchase #2 $103.35   9.467%   $113.1341   $113.13   $113.15   $113.10  
  Purchase #3 $71.73   6.786%   $76.5976   $76.60   $76.60   $76.60  
  Purchase #4 $79.41   9.113%   $86.6466   $86.65   $86.65   $86.60  
  Purchase #5 $37.51   3.618%   $38.8671   $38.87   $38.85   $38.90  
  Purchase #6 $16.81   13.779%   $19.1262   $19.13   $19.15   $19.10  
  Purchase #7 $155.65   5.513%   $164.231   $164.23   $164.25   $164.20  
  7 purchase totals = $526.29       $567.9338   $567.94   $568.00   $567.80