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 $39.46   11.397%   $43.9573   $43.96   $43.95   $44.00  
  Purchase #2 $98.69   8.760%   $107.3352   $107.34   $107.35   $107.30  
  Purchase #3 $72.93   12.620%   $82.1338   $82.13   $82.15   $82.10  
  Purchase #4 $159.27   9.176%   $173.8846   $173.88   $173.90   $173.90  
  Purchase #5 $165.84   11.554%   $185.0012   $185.00   $185.00   $185.00  
  Purchase #6 $89.86   3.862%   $93.3304   $93.33   $93.35   $93.30  
  Purchase #7 $70.55   7.269%   $75.6783   $75.68   $75.70   $75.70  
  7 purchase totals = $696.60       $761.3208   $761.32   $761.40   $761.30