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 $93.68   11.764%   $104.7005   $104.70   $104.70   $104.70  
  Purchase #2 $16.79   6.698%   $17.9146   $17.91   $17.90   $17.90  
  Purchase #3 $120.36   11.174%   $133.809   $133.81   $133.80   $133.80  
  Purchase #4 $29.26   12.794%   $33.0035   $33.00   $33.00   $33.00  
  Purchase #5 $90.83   6.292%   $96.545   $96.55   $96.55   $96.50  
  Purchase #6 $72.89   10.576%   $80.5988   $80.60   $80.60   $80.60  
  Purchase #7 $207.98   4.275%   $216.8711   $216.87   $216.85   $216.90  
  7 purchase totals = $631.79       $683.4425   $683.44   $683.40   $683.40