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 $107.81   10.271%   $118.8832   $118.88   $118.90   $118.90  
  Purchase #2 $195.31   11.743%   $218.2453   $218.25   $218.25   $218.20  
  Purchase #3 $14.83   6.221%   $15.7526   $15.75   $15.75   $15.80  
  Purchase #4 $179.48   12.520%   $201.9509   $201.95   $201.95   $202.00  
  Purchase #5 $91.95   5.357%   $96.8758   $96.88   $96.90   $96.90  
  Purchase #6 $124.29   10.641%   $137.5157   $137.52   $137.50   $137.50  
  Purchase #7 $193.76   11.273%   $215.6026   $215.60   $215.60   $215.60  
  7 purchase totals = $907.43       $1,004.8261   $1,004.83   $1,004.85   $1,004.90