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 $86.46   8.591%   $93.8878   $93.89   $93.90   $93.90  
  Purchase #2 $250.28   10.854%   $277.4454   $277.45   $277.45   $277.40  
  Purchase #3 $230.79   3.768%   $239.4862   $239.49   $239.50   $239.50  
  Purchase #4 $153.78   6.806%   $164.2463   $164.25   $164.25   $164.20  
  Purchase #5 $98.90   12.797%   $111.5562   $111.56   $111.55   $111.60  
  Purchase #6 $181.51   7.388%   $194.92   $194.92   $194.90   $194.90  
  Purchase #7 $75.37   5.142%   $79.2455   $79.25   $79.25   $79.20  
  7 purchase totals = $1,077.09       $1,160.7874   $1,160.81   $1,160.80   $1,160.70