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 $63.48   4.698%   $66.4623   $66.46   $66.45   $66.50  
  Purchase #2 $101.96   8.127%   $110.2463   $110.25   $110.25   $110.20  
  Purchase #3 $5.65   3.848%   $5.8674   $5.87   $5.85   $5.90  
  Purchase #4 $46.38   13.417%   $52.6028   $52.60   $52.60   $52.60  
  Purchase #5 $179.92   13.403%   $204.0347   $204.03   $204.05   $204.00  
  Purchase #6 $147.28   11.384%   $164.0464   $164.05   $164.05   $164.00  
  Purchase #7 $142.31   4.226%   $148.324   $148.32   $148.30   $148.30  
  7 purchase totals = $686.98       $751.5839   $751.58   $751.55   $751.50