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 $42.95   4.144%   $44.7298   $44.73   $44.75   $44.70  
  Purchase #2 $158.87   3.605%   $164.5973   $164.60   $164.60   $164.60  
  Purchase #3 $50.57   12.382%   $56.8316   $56.83   $56.85   $56.80  
  Purchase #4 $70.65   3.316%   $72.9928   $72.99   $73.00   $73.00  
  Purchase #5 $193.48   5.671%   $204.4523   $204.45   $204.45   $204.50  
  Purchase #6 $175.29   11.225%   $194.9663   $194.97   $194.95   $195.00  
  Purchase #7 $250.52   11.662%   $279.7356   $279.74   $279.75   $279.70  
  7 purchase totals = $942.33       $1,018.3057   $1,018.31   $1,018.35   $1,018.30