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 $213.48   6.389%   $227.1192   $227.12   $227.10   $227.10  
  Purchase #2 $38.98   4.454%   $40.7162   $40.72   $40.70   $40.70  
  Purchase #3 $157.36   6.284%   $167.2485   $167.25   $167.25   $167.20  
  Purchase #4 $97.52   8.754%   $106.0569   $106.06   $106.05   $106.10  
  Purchase #5 $131.54   5.665%   $138.9917   $138.99   $139.00   $139.00  
  Purchase #6 $172.74   12.102%   $193.645   $193.65   $193.65   $193.60  
  Purchase #7 $87.52   5.152%   $92.029   $92.03   $92.05   $92.00  
  7 purchase totals = $899.14       $965.8065   $965.82   $965.80   $965.70