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 $145.69   4.216%   $151.8323   $151.83   $151.85   $151.80  
  Purchase #2 $227.83   5.870%   $241.2036   $241.20   $241.20   $241.20  
  Purchase #3 $175.65   5.243%   $184.8593   $184.86   $184.85   $184.90  
  Purchase #4 $83.73   13.440%   $94.9833   $94.98   $95.00   $95.00  
  Purchase #5 $96.92   13.486%   $109.9906   $109.99   $110.00   $110.00  
  Purchase #6 $223.40   12.581%   $251.506   $251.51   $251.50   $251.50  
  Purchase #7 $33.60   4.310%   $35.0482   $35.05   $35.05   $35.00  
  7 purchase totals = $986.82       $1,069.4233   $1,069.42   $1,069.45   $1,069.40