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 $71.30   5.654%   $75.3313   $75.33   $75.35   $75.30  
  Purchase #2 $89.65   6.236%   $95.2406   $95.24   $95.25   $95.20  
  Purchase #3 $12.67   12.358%   $14.2358   $14.24   $14.25   $14.20  
  Purchase #4 $234.37   3.868%   $243.4354   $243.44   $243.45   $243.40  
  Purchase #5 $107.89   12.433%   $121.304   $121.30   $121.30   $121.30  
  Purchase #6 $118.80   7.242%   $127.4035   $127.40   $127.40   $127.40  
  Purchase #7 $168.61   10.209%   $185.8234   $185.82   $185.80   $185.80  
  7 purchase totals = $803.29       $862.7740   $862.77   $862.80   $862.60