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 $212.75   5.160%   $223.7279   $223.73   $223.75   $223.70  
  Purchase #2 $72.36   9.657%   $79.3478   $79.35   $79.35   $79.30  
  Purchase #3 $61.46   7.846%   $66.2822   $66.28   $66.30   $66.30  
  Purchase #4 $203.94   5.249%   $214.6448   $214.64   $214.65   $214.60  
  Purchase #5 $68.54   9.457%   $75.0218   $75.02   $75.00   $75.00  
  Purchase #6 $229.69   13.123%   $259.8322   $259.83   $259.85   $259.80  
  Purchase #7 $103.66   10.642%   $114.6915   $114.69   $114.70   $114.70  
  7 purchase totals = $952.40       $1,033.5482   $1,033.54   $1,033.60   $1,033.40