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 $55.97   13.585%   $63.5735   $63.57   $63.55   $63.60  
  Purchase #2 $211.51   7.806%   $228.0205   $228.02   $228.00   $228.00  
  Purchase #3 $214.40   7.177%   $229.7875   $229.79   $229.80   $229.80  
  Purchase #4 $123.57   9.675%   $135.5254   $135.53   $135.55   $135.50  
  Purchase #5 $176.40   12.554%   $198.5453   $198.55   $198.55   $198.50  
  Purchase #6 $188.46   5.571%   $198.9591   $198.96   $198.95   $199.00  
  Purchase #7 $212.47   9.479%   $232.61   $232.61   $232.60   $232.60  
  7 purchase totals = $1,182.78       $1,287.0213   $1,287.03   $1,287.00   $1,287.00