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 $238.52   12.104%   $267.3905   $267.39   $267.40   $267.40  
  Purchase #2 $181.42   11.109%   $201.5739   $201.57   $201.55   $201.60  
  Purchase #3 $127.41   8.867%   $138.7074   $138.71   $138.70   $138.70  
  Purchase #4 $140.47   11.645%   $156.8277   $156.83   $156.85   $156.80  
  Purchase #5 $112.69   10.414%   $124.4255   $124.43   $124.45   $124.40  
  Purchase #6 $48.97   12.796%   $55.2362   $55.24   $55.25   $55.20  
  Purchase #7 $188.43   9.205%   $205.775   $205.78   $205.80   $205.80  
  7 purchase totals = $1,037.91       $1,149.9362   $1,149.95   $1,150.00   $1,149.90