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 $63.74   5.102%   $66.992   $66.99   $67.00   $67.00  
  Purchase #2 $95.65   11.491%   $106.6411   $106.64   $106.65   $106.60  
  Purchase #3 $67.78   7.728%   $73.018   $73.02   $73.00   $73.00  
  Purchase #4 $115.75   12.277%   $129.9606   $129.96   $129.95   $130.00  
  Purchase #5 $67.38   5.467%   $71.0637   $71.06   $71.05   $71.10  
  Purchase #6 $61.35   10.146%   $67.5746   $67.57   $67.55   $67.60  
  Purchase #7 $157.84   9.386%   $172.6549   $172.65   $172.65   $172.70  
  7 purchase totals = $629.49       $687.9049   $687.89   $687.85   $688.00