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 $93.51   3.122%   $96.4294   $96.43   $96.45   $96.40  
  Purchase #2 $177.92   12.268%   $199.7472   $199.75   $199.75   $199.70  
  Purchase #3 $231.31   4.838%   $242.5008   $242.50   $242.50   $242.50  
  Purchase #4 $54.25   4.572%   $56.7303   $56.73   $56.75   $56.70  
  Purchase #5 $205.53   9.450%   $224.9526   $224.95   $224.95   $225.00  
  Purchase #6 $155.97   10.491%   $172.3328   $172.33   $172.35   $172.30  
  Purchase #7 $27.96   12.183%   $31.3664   $31.37   $31.35   $31.40  
  7 purchase totals = $946.45       $1,024.0595   $1,024.06   $1,024.10   $1,024.00