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 $23.73   5.478%   $25.0299   $25.03   $25.05   $25.00  
  Purchase #2 $153.51   8.588%   $166.6934   $166.69   $166.70   $166.70  
  Purchase #3 $66.47   9.861%   $73.0246   $73.02   $73.00   $73.00  
  Purchase #4 $226.33   11.168%   $251.6065   $251.61   $251.60   $251.60  
  Purchase #5 $112.77   12.626%   $127.0083   $127.01   $127.00   $127.00  
  Purchase #6 $181.74   6.375%   $193.3259   $193.33   $193.35   $193.30  
  Purchase #7 $10.73   12.670%   $12.0895   $12.09   $12.10   $12.10  
  7 purchase totals = $775.28       $848.7781   $848.78   $848.80   $848.70