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 $52.95   7.143%   $56.7322   $56.73   $56.75   $56.70  
  Purchase #2 $214.57   8.601%   $233.0252   $233.03   $233.05   $233.00  
  Purchase #3 $94.49   6.273%   $100.4174   $100.42   $100.40   $100.40  
  Purchase #4 $218.65   11.362%   $243.493   $243.49   $243.50   $243.50  
  Purchase #5 $36.69   11.311%   $40.84   $40.84   $40.85   $40.80  
  Purchase #6 $68.42   9.295%   $74.7796   $74.78   $74.80   $74.80  
  Purchase #7 $241.85   4.236%   $252.0948   $252.09   $252.10   $252.10  
  7 purchase totals = $927.62       $1,001.3822   $1,001.38   $1,001.45   $1,001.30