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 $90.39   8.748%   $98.2973   $98.30   $98.30   $98.30  
  Purchase #2 $190.31   4.181%   $198.2669   $198.27   $198.25   $198.30  
  Purchase #3 $134.95   11.506%   $150.4773   $150.48   $150.50   $150.50  
  Purchase #4 $68.46   8.312%   $74.1504   $74.15   $74.15   $74.20  
  Purchase #5 $204.94   8.527%   $222.4152   $222.42   $222.40   $222.40  
  Purchase #6 $29.60   5.623%   $31.2644   $31.26   $31.25   $31.30  
  Purchase #7 $235.32   7.319%   $252.5431   $252.54   $252.55   $252.50  
  7 purchase totals = $953.97       $1,027.4146   $1,027.42   $1,027.40   $1,027.50