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 $76.65   10.278%   $84.5281   $84.53   $84.55   $84.50  
  Purchase #2 $238.66   3.308%   $246.5549   $246.55   $246.55   $246.60  
  Purchase #3 $216.46   7.736%   $233.2053   $233.21   $233.20   $233.20  
  Purchase #4 $5.70   5.609%   $6.0197   $6.02   $6.00   $6.00  
  Purchase #5 $40.26   4.363%   $42.0165   $42.02   $42.00   $42.00  
  Purchase #6 $232.75   13.293%   $263.6895   $263.69   $263.70   $263.70  
  Purchase #7 $157.77   9.513%   $172.7787   $172.78   $172.80   $172.80  
  7 purchase totals = $968.25       $1,048.7927   $1,048.80   $1,048.80   $1,048.80