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 $239.85   10.819%   $265.7994   $265.80   $265.80   $265.80  
  Purchase #2 $153.65   8.111%   $166.1126   $166.11   $166.10   $166.10  
  Purchase #3 $211.32   6.162%   $224.3415   $224.34   $224.35   $224.30  
  Purchase #4 $100.60   6.376%   $107.0143   $107.01   $107.00   $107.00  
  Purchase #5 $68.87   12.608%   $77.5531   $77.55   $77.55   $77.60  
  Purchase #6 $148.43   13.309%   $168.1845   $168.18   $168.20   $168.20  
  Purchase #7 $134.33   10.279%   $148.1378   $148.14   $148.15   $148.10  
  7 purchase totals = $1,057.05       $1,157.1432   $1,157.13   $1,157.15   $1,157.10