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 $182.48   10.149%   $200.9999   $201.00   $201.00   $201.00  
  Purchase #2 $90.83   6.391%   $96.6349   $96.63   $96.65   $96.60  
  Purchase #3 $148.95   10.693%   $164.8772   $164.88   $164.90   $164.90  
  Purchase #4 $245.25   12.408%   $275.6806   $275.68   $275.70   $275.70  
  Purchase #5 $157.98   8.540%   $171.4715   $171.47   $171.45   $171.50  
  Purchase #6 $148.51   11.405%   $165.4476   $165.45   $165.45   $165.40  
  Purchase #7 $71.43   4.603%   $74.7179   $74.72   $74.70   $74.70  
  7 purchase totals = $1,045.43       $1,149.8296   $1,149.83   $1,149.85   $1,149.80