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 $52.33   5.723%   $55.3248   $55.32   $55.30   $55.30  
  Purchase #2 $79.26   11.687%   $88.5231   $88.52   $88.50   $88.50  
  Purchase #3 $103.75   10.106%   $114.235   $114.24   $114.25   $114.20  
  Purchase #4 $102.44   6.142%   $108.7319   $108.73   $108.75   $108.70  
  Purchase #5 $81.39   6.343%   $86.5526   $86.55   $86.55   $86.60  
  Purchase #6 $206.58   8.436%   $224.0071   $224.01   $224.00   $224.00  
  Purchase #7 $193.79   5.744%   $204.9213   $204.92   $204.90   $204.90  
  7 purchase totals = $819.54       $882.2958   $882.29   $882.25   $882.20