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 $151.59   12.623%   $170.7252   $170.73   $170.75   $170.70  
  Purchase #2 $96.47   10.176%   $106.2868   $106.29   $106.30   $106.30  
  Purchase #3 $155.91   9.260%   $170.3473   $170.35   $170.35   $170.30  
  Purchase #4 $206.27   8.852%   $224.529   $224.53   $224.55   $224.50  
  Purchase #5 $152.60   9.857%   $167.6418   $167.64   $167.65   $167.60  
  Purchase #6 $32.30   6.393%   $34.3649   $34.36   $34.35   $34.40  
  Purchase #7 $59.78   3.381%   $61.8012   $61.80   $61.80   $61.80  
  7 purchase totals = $854.92       $935.6962   $935.70   $935.75   $935.60