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 $234.39   11.225%   $260.7003   $260.70   $260.70   $260.70  
  Purchase #2 $156.76   7.249%   $168.1235   $168.12   $168.10   $168.10  
  Purchase #3 $80.85   6.191%   $85.8554   $85.86   $85.85   $85.90  
  Purchase #4 $154.55   6.484%   $164.571   $164.57   $164.55   $164.60  
  Purchase #5 $23.55   8.604%   $25.5762   $25.58   $25.60   $25.60  
  Purchase #6 $205.60   8.802%   $223.6969   $223.70   $223.70   $223.70  
  Purchase #7 $95.26   3.368%   $98.4684   $98.47   $98.45   $98.50  
  7 purchase totals = $950.96       $1,026.9917   $1,027.00   $1,026.95   $1,027.10