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 $82.91   11.706%   $92.6154   $92.62   $92.60   $92.60  
  Purchase #2 $31.86   9.399%   $34.8545   $34.85   $34.85   $34.90  
  Purchase #3 $195.93   10.224%   $215.9619   $215.96   $215.95   $216.00  
  Purchase #4 $155.85   6.414%   $165.8462   $165.85   $165.85   $165.80  
  Purchase #5 $47.35   10.171%   $52.166   $52.17   $52.15   $52.20  
  Purchase #6 $143.62   12.105%   $161.0052   $161.01   $161.00   $161.00  
  Purchase #7 $74.58   8.371%   $80.8231   $80.82   $80.80   $80.80  
  7 purchase totals = $732.10       $803.2723   $803.28   $803.20   $803.30