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 $61.50   8.437%   $66.6888   $66.69   $66.70   $66.70  
  Purchase #2 $106.30   5.669%   $112.3261   $112.33   $112.35   $112.30  
  Purchase #3 $69.47   6.848%   $74.2273   $74.23   $74.25   $74.20  
  Purchase #4 $64.80   8.116%   $70.0592   $70.06   $70.05   $70.10  
  Purchase #5 $183.62   6.790%   $196.0878   $196.09   $196.10   $196.10  
  Purchase #6 $41.50   7.402%   $44.5718   $44.57   $44.55   $44.60  
  Purchase #7 $165.37   7.764%   $178.2093   $178.21   $178.20   $178.20  
  7 purchase totals = $692.56       $742.1703   $742.18   $742.20   $742.20