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 $204.31   5.103%   $214.7359   $214.74   $214.75   $214.70  
  Purchase #2 $50.74   3.463%   $52.4971   $52.50   $52.50   $52.50  
  Purchase #3 $58.45   12.255%   $65.613   $65.61   $65.60   $65.60  
  Purchase #4 $206.67   6.198%   $219.4794   $219.48   $219.50   $219.50  
  Purchase #5 $219.48   3.426%   $226.9994   $227.00   $227.00   $227.00  
  Purchase #6 $28.64   8.135%   $30.9699   $30.97   $30.95   $31.00  
  Purchase #7 $142.47   7.158%   $152.668   $152.67   $152.65   $152.70  
  7 purchase totals = $910.76       $962.9627   $962.97   $962.95   $963.00