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 $53.35   5.434%   $56.249   $56.25   $56.25   $56.20  
  Purchase #2 $65.98   4.252%   $68.7855   $68.79   $68.80   $68.80  
  Purchase #3 $104.26   5.256%   $109.7399   $109.74   $109.75   $109.70  
  Purchase #4 $47.66   5.162%   $50.1202   $50.12   $50.10   $50.10  
  Purchase #5 $147.87   13.327%   $167.5766   $167.58   $167.60   $167.60  
  Purchase #6 $180.57   4.629%   $188.9286   $188.93   $188.95   $188.90  
  Purchase #7 $224.41   9.115%   $244.865   $244.87   $244.85   $244.90  
  7 purchase totals = $824.10       $886.2648   $886.28   $886.30   $886.20