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 $42.90   4.754%   $44.9395   $44.94   $44.95   $44.90  
  Purchase #2 $40.28   3.335%   $41.6233   $41.62   $41.60   $41.60  
  Purchase #3 $120.32   12.574%   $135.449   $135.45   $135.45   $135.40  
  Purchase #4 $202.48   4.332%   $211.2514   $211.25   $211.25   $211.30  
  Purchase #5 $165.72   8.803%   $180.3083   $180.31   $180.30   $180.30  
  Purchase #6 $170.93   13.486%   $193.9816   $193.98   $194.00   $194.00  
  Purchase #7 $204.28   5.626%   $215.7728   $215.77   $215.75   $215.80  
  7 purchase totals = $946.91       $1,023.3259   $1,023.32   $1,023.30   $1,023.30