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 $58.56   12.645%   $65.9649   $65.96   $65.95   $66.00  
  Purchase #2 $5.64   9.686%   $6.1863   $6.19   $6.20   $6.20  
  Purchase #3 $149.56   10.654%   $165.4941   $165.49   $165.50   $165.50  
  Purchase #4 $24.83   6.248%   $26.3814   $26.38   $26.40   $26.40  
  Purchase #5 $87.85   6.508%   $93.5673   $93.57   $93.55   $93.60  
  Purchase #6 $241.25   4.539%   $252.2003   $252.20   $252.20   $252.20  
  Purchase #7 $141.78   10.833%   $157.139   $157.14   $157.15   $157.10  
  7 purchase totals = $709.47       $766.9333   $766.93   $766.95   $767.00