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 $179.68   3.523%   $186.0101   $186.01   $186.00   $186.00  
  Purchase #2 $19.52   8.807%   $21.2391   $21.24   $21.25   $21.20  
  Purchase #3 $129.95   9.281%   $142.0107   $142.01   $142.00   $142.00  
  Purchase #4 $72.70   11.232%   $80.8657   $80.87   $80.85   $80.90  
  Purchase #5 $248.39   7.296%   $266.5125   $266.51   $266.50   $266.50  
  Purchase #6 $198.45   7.691%   $213.7128   $213.71   $213.70   $213.70  
  Purchase #7 $37.54   5.740%   $39.6948   $39.69   $39.70   $39.70  
  7 purchase totals = $886.23       $950.0457   $950.04   $950.00   $950.00