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 $88.86   6.111%   $94.2902   $94.29   $94.30   $94.30  
  Purchase #2 $183.71   9.330%   $200.8501   $200.85   $200.85   $200.90  
  Purchase #3 $200.62   12.203%   $225.1017   $225.10   $225.10   $225.10  
  Purchase #4 $81.84   5.483%   $86.3273   $86.33   $86.35   $86.30  
  Purchase #5 $81.72   7.357%   $87.7321   $87.73   $87.75   $87.70  
  Purchase #6 $67.31   4.860%   $70.5813   $70.58   $70.60   $70.60  
  Purchase #7 $237.88   8.685%   $258.5399   $258.54   $258.55   $258.50  
  7 purchase totals = $941.94       $1,023.4226   $1,023.42   $1,023.50   $1,023.40