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 $88.62   9.347%   $96.9033   $96.90   $96.90   $96.90  
  Purchase #2 $218.37   11.729%   $243.9826   $243.98   $244.00   $244.00  
  Purchase #3 $221.43   10.343%   $244.3325   $244.33   $244.35   $244.30  
  Purchase #4 $190.44   4.387%   $198.7946   $198.79   $198.80   $198.80  
  Purchase #5 $23.32   12.660%   $26.2723   $26.27   $26.25   $26.30  
  Purchase #6 $148.47   4.815%   $155.6188   $155.62   $155.60   $155.60  
  Purchase #7 $241.69   9.212%   $263.9545   $263.95   $263.95   $264.00  
  7 purchase totals = $1,132.34       $1,229.8586   $1,229.84   $1,229.85   $1,229.90