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 $156.45   4.842%   $164.0253   $164.03   $164.05   $164.00  
  Purchase #2 $218.35   13.131%   $247.0215   $247.02   $247.00   $247.00  
  Purchase #3 $11.31   3.585%   $11.7155   $11.72   $11.70   $11.70  
  Purchase #4 $240.95   9.559%   $263.9824   $263.98   $264.00   $264.00  
  Purchase #5 $48.85   8.313%   $52.9109   $52.91   $52.90   $52.90  
  Purchase #6 $192.44   4.789%   $201.656   $201.66   $201.65   $201.70  
  Purchase #7 $205.56   6.260%   $218.4281   $218.43   $218.45   $218.40  
  7 purchase totals = $1,073.91       $1,159.7397   $1,159.75   $1,159.75   $1,159.70