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 $164.44   12.286%   $184.6431   $184.64   $184.65   $184.60  
  Purchase #2 $180.48   3.530%   $186.8509   $186.85   $186.85   $186.90  
  Purchase #3 $94.86   5.466%   $100.045   $100.05   $100.05   $100.00  
  Purchase #4 $211.78   5.824%   $224.1141   $224.11   $224.10   $224.10  
  Purchase #5 $93.40   3.102%   $96.2973   $96.30   $96.30   $96.30  
  Purchase #6 $187.75   8.478%   $203.6674   $203.67   $203.65   $203.70  
  Purchase #7 $40.26   5.662%   $42.5395   $42.54   $42.55   $42.50  
  7 purchase totals = $972.97       $1,038.1573   $1,038.16   $1,038.15   $1,038.10