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 $88.59   8.609%   $96.2167   $96.22   $96.20   $96.20  
  Purchase #2 $223.43   6.833%   $238.697   $238.70   $238.70   $238.70  
  Purchase #3 $134.35   13.506%   $152.4953   $152.50   $152.50   $152.50  
  Purchase #4 $216.88   7.251%   $232.606   $232.61   $232.60   $232.60  
  Purchase #5 $10.68   13.859%   $12.1601   $12.16   $12.15   $12.20  
  Purchase #6 $94.63   13.337%   $107.2508   $107.25   $107.25   $107.30  
  Purchase #7 $227.68   13.140%   $257.5972   $257.60   $257.60   $257.60  
  7 purchase totals = $996.24       $1,097.0231   $1,097.04   $1,097.00   $1,097.10