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 $177.66   13.495%   $201.6352   $201.64   $201.65   $201.60  
  Purchase #2 $170.91   13.119%   $193.3317   $193.33   $193.35   $193.30  
  Purchase #3 $11.56   4.188%   $12.0441   $12.04   $12.05   $12.00  
  Purchase #4 $103.41   12.415%   $116.2484   $116.25   $116.25   $116.20  
  Purchase #5 $17.46   10.596%   $19.3101   $19.31   $19.30   $19.30  
  Purchase #6 $5.91   10.231%   $6.5147   $6.51   $6.50   $6.50  
  Purchase #7 $204.97   9.351%   $224.1367   $224.14   $224.15   $224.10  
  7 purchase totals = $691.88       $773.2209   $773.22   $773.25   $773.00