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 $58.74   12.301%   $65.9656   $65.97   $65.95   $66.00  
  Purchase #2 $156.33   7.502%   $168.0579   $168.06   $168.05   $168.10  
  Purchase #3 $214.25   7.442%   $230.1945   $230.19   $230.20   $230.20  
  Purchase #4 $56.29   8.314%   $60.97   $60.97   $60.95   $61.00  
  Purchase #5 $65.74   11.360%   $73.2081   $73.21   $73.20   $73.20  
  Purchase #6 $159.75   10.854%   $177.0893   $177.09   $177.10   $177.10  
  Purchase #7 $54.34   9.626%   $59.5708   $59.57   $59.55   $59.60  
  7 purchase totals = $765.44       $835.0562   $835.06   $835.00   $835.20