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 $98.66   7.465%   $106.025   $106.03   $106.05   $106.00  
  Purchase #2 $60.66   13.356%   $68.7617   $68.76   $68.75   $68.80  
  Purchase #3 $200.37   12.560%   $225.5365   $225.54   $225.55   $225.50  
  Purchase #4 $175.57   8.655%   $190.7656   $190.77   $190.75   $190.80  
  Purchase #5 $132.49   13.153%   $149.9164   $149.92   $149.90   $149.90  
  Purchase #6 $220.37   3.292%   $227.6246   $227.62   $227.60   $227.60  
  Purchase #7 $221.27   6.361%   $235.345   $235.35   $235.35   $235.30  
  7 purchase totals = $1,109.39       $1,203.9748   $1,203.99   $1,203.95   $1,203.90