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 $235.41   10.118%   $259.2288   $259.23   $259.25   $259.20  
  Purchase #2 $173.70   8.571%   $188.5878   $188.59   $188.60   $188.60  
  Purchase #3 $48.39   5.320%   $50.9643   $50.96   $50.95   $51.00  
  Purchase #4 $177.69   9.391%   $194.3769   $194.38   $194.40   $194.40  
  Purchase #5 $221.80   12.577%   $249.6958   $249.70   $249.70   $249.70  
  Purchase #6 $10.97   6.107%   $11.6399   $11.64   $11.65   $11.60  
  Purchase #7 $190.60   6.226%   $202.4668   $202.47   $202.45   $202.50  
  7 purchase totals = $1,058.56       $1,156.9603   $1,156.97   $1,157.00   $1,157.00