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 $250.98   3.434%   $259.5987   $259.60   $259.60   $259.60  
  Purchase #2 $73.36   3.115%   $75.6452   $75.65   $75.65   $75.60  
  Purchase #3 $60.72   11.464%   $67.6809   $67.68   $67.70   $67.70  
  Purchase #4 $86.63   7.142%   $92.8171   $92.82   $92.80   $92.80  
  Purchase #5 $131.50   10.709%   $145.5823   $145.58   $145.60   $145.60  
  Purchase #6 $238.62   13.767%   $271.4708   $271.47   $271.45   $271.50  
  Purchase #7 $193.59   4.281%   $201.8776   $201.88   $201.90   $201.90  
  7 purchase totals = $1,035.40       $1,114.6726   $1,114.68   $1,114.70   $1,114.70