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 $168.67   10.818%   $186.9167   $186.92   $186.90   $186.90  
  Purchase #2 $240.57   11.280%   $267.7063   $267.71   $267.70   $267.70  
  Purchase #3 $153.50   3.184%   $158.3874   $158.39   $158.40   $158.40  
  Purchase #4 $202.46   8.696%   $220.0659   $220.07   $220.05   $220.10  
  Purchase #5 $25.39   4.639%   $26.5678   $26.57   $26.55   $26.60  
  Purchase #6 $95.32   12.115%   $106.868   $106.87   $106.85   $106.90  
  Purchase #7 $248.66   13.576%   $282.4181   $282.42   $282.40   $282.40  
  7 purchase totals = $1,134.57       $1,248.9302   $1,248.95   $1,248.85   $1,249.00