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 $186.61   6.399%   $198.5512   $198.55   $198.55   $198.60  
  Purchase #2 $232.80   6.487%   $247.9017   $247.90   $247.90   $247.90  
  Purchase #3 $65.40   4.412%   $68.2854   $68.29   $68.30   $68.30  
  Purchase #4 $203.97   10.285%   $224.9483   $224.95   $224.95   $224.90  
  Purchase #5 $66.66   13.417%   $75.6038   $75.60   $75.60   $75.60  
  Purchase #6 $86.74   5.355%   $91.3849   $91.38   $91.40   $91.40  
  Purchase #7 $149.67   3.436%   $154.8127   $154.81   $154.80   $154.80  
  7 purchase totals = $991.85       $1,061.4880   $1,061.48   $1,061.50   $1,061.50