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 $112.44   8.773%   $122.3044   $122.30   $122.30   $122.30  
  Purchase #2 $139.93   8.613%   $151.9822   $151.98   $152.00   $152.00  
  Purchase #3 $109.59   11.844%   $122.5698   $122.57   $122.55   $122.60  
  Purchase #4 $191.63   11.649%   $213.953   $213.95   $213.95   $214.00  
  Purchase #5 $204.61   12.474%   $230.1331   $230.13   $230.15   $230.10  
  Purchase #6 $47.26   9.714%   $51.8508   $51.85   $51.85   $51.90  
  Purchase #7 $182.74   7.266%   $196.0179   $196.02   $196.00   $196.00  
  7 purchase totals = $988.20       $1,088.8112   $1,088.80   $1,088.80   $1,088.90