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 $231.57   12.134%   $259.6687   $259.67   $259.65   $259.70  
  Purchase #2 $214.61   6.703%   $228.9953   $229.00   $229.00   $229.00  
  Purchase #3 $86.42   6.396%   $91.9474   $91.95   $91.95   $91.90  
  Purchase #4 $224.57   4.435%   $234.5297   $234.53   $234.55   $234.50  
  Purchase #5 $44.28   4.156%   $46.1203   $46.12   $46.10   $46.10  
  Purchase #6 $75.95   10.614%   $84.0113   $84.01   $84.00   $84.00  
  Purchase #7 $49.32   11.189%   $54.8384   $54.84   $54.85   $54.80  
  7 purchase totals = $926.72       $1,000.1111   $1,000.12   $1,000.10   $1,000.00