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 $247.52   6.275%   $263.0519   $263.05   $263.05   $263.10  
  Purchase #2 $60.98   7.686%   $65.6669   $65.67   $65.65   $65.70  
  Purchase #3 $183.93   7.587%   $197.8848   $197.88   $197.90   $197.90  
  Purchase #4 $114.96   3.642%   $119.1468   $119.15   $119.15   $119.10  
  Purchase #5 $69.74   6.710%   $74.4196   $74.42   $74.40   $74.40  
  Purchase #6 $123.41   6.518%   $131.4539   $131.45   $131.45   $131.50  
  Purchase #7 $80.45   4.347%   $83.9472   $83.95   $83.95   $83.90  
  7 purchase totals = $880.99       $935.5711   $935.57   $935.55   $935.60