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 $187.88   10.262%   $207.1602   $207.16   $207.15   $207.20  
  Purchase #2 $118.44   5.127%   $124.5124   $124.51   $124.50   $124.50  
  Purchase #3 $69.86   8.249%   $75.6228   $75.62   $75.60   $75.60  
  Purchase #4 $173.57   6.285%   $184.4789   $184.48   $184.50   $184.50  
  Purchase #5 $130.28   7.174%   $139.6263   $139.63   $139.65   $139.60  
  Purchase #6 $235.33   11.646%   $262.7365   $262.74   $262.75   $262.70  
  Purchase #7 $36.80   3.806%   $38.2006   $38.20   $38.20   $38.20  
  7 purchase totals = $952.16       $1,032.3377   $1,032.34   $1,032.35   $1,032.30