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 $140.41   11.286%   $156.2567   $156.26   $156.25   $156.30  
  Purchase #2 $103.75   11.450%   $115.6294   $115.63   $115.65   $115.60  
  Purchase #3 $165.63   5.363%   $174.5127   $174.51   $174.50   $174.50  
  Purchase #4 $184.61   9.192%   $201.5794   $201.58   $201.60   $201.60  
  Purchase #5 $116.36   10.136%   $128.1542   $128.15   $128.15   $128.20  
  Purchase #6 $224.85   6.622%   $239.7396   $239.74   $239.75   $239.70  
  Purchase #7 $8.95   5.342%   $9.4281   $9.43   $9.45   $9.40  
  7 purchase totals = $944.56       $1,025.3001   $1,025.30   $1,025.35   $1,025.30