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 $60.96   7.107%   $65.2924   $65.29   $65.30   $65.30  
  Purchase #2 $242.50   11.285%   $269.8661   $269.87   $269.85   $269.90  
  Purchase #3 $47.62   10.209%   $52.4815   $52.48   $52.50   $52.50  
  Purchase #4 $161.39   3.790%   $167.5067   $167.51   $167.50   $167.50  
  Purchase #5 $194.36   9.232%   $212.3033   $212.30   $212.30   $212.30  
  Purchase #6 $88.71   9.815%   $97.4169   $97.42   $97.40   $97.40  
  Purchase #7 $86.70   13.242%   $98.1808   $98.18   $98.20   $98.20  
  7 purchase totals = $882.24       $963.0477   $963.05   $963.05   $963.10