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 $185.86   8.166%   $201.0373   $201.04   $201.05   $201.00  
  Purchase #2 $36.62   5.189%   $38.5202   $38.52   $38.50   $38.50  
  Purchase #3 $50.90   8.434%   $55.1929   $55.19   $55.20   $55.20  
  Purchase #4 $175.62   4.356%   $183.27   $183.27   $183.25   $183.30  
  Purchase #5 $8.48   5.637%   $8.958   $8.96   $8.95   $9.00  
  Purchase #6 $175.55   4.620%   $183.6604   $183.66   $183.65   $183.70  
  Purchase #7 $202.56   4.687%   $212.054   $212.05   $212.05   $212.10  
  7 purchase totals = $835.59       $882.6928   $882.69   $882.65   $882.80