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 $98.94   6.732%   $105.6006   $105.60   $105.60   $105.60  
  Purchase #2 $204.38   6.831%   $218.3412   $218.34   $218.35   $218.30  
  Purchase #3 $195.71   8.835%   $213.001   $213.00   $213.00   $213.00  
  Purchase #4 $33.30   7.245%   $35.7126   $35.71   $35.70   $35.70  
  Purchase #5 $203.48   12.837%   $229.6007   $229.60   $229.60   $229.60  
  Purchase #6 $162.77   12.450%   $183.0349   $183.03   $183.05   $183.00  
  Purchase #7 $43.94   7.866%   $47.3963   $47.40   $47.40   $47.40  
  7 purchase totals = $942.52       $1,032.6873   $1,032.68   $1,032.70   $1,032.60