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 $226.54   8.155%   $245.0143   $245.01   $245.00   $245.00  
  Purchase #2 $153.99   6.714%   $164.3289   $164.33   $164.35   $164.30  
  Purchase #3 $180.65   8.804%   $196.5544   $196.55   $196.55   $196.60  
  Purchase #4 $109.69   6.425%   $116.7376   $116.74   $116.75   $116.70  
  Purchase #5 $244.86   11.354%   $272.6614   $272.66   $272.65   $272.70  
  Purchase #6 $103.73   6.141%   $110.1001   $110.10   $110.10   $110.10  
  Purchase #7 $143.58   6.470%   $152.8696   $152.87   $152.85   $152.90  
  7 purchase totals = $1,163.04       $1,258.2663   $1,258.26   $1,258.25   $1,258.30