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 $217.74   12.489%   $244.9335   $244.93   $244.95   $244.90  
  Purchase #2 $163.41   7.315%   $175.3634   $175.36   $175.35   $175.40  
  Purchase #3 $102.47   4.522%   $107.1037   $107.10   $107.10   $107.10  
  Purchase #4 $99.85   6.410%   $106.2504   $106.25   $106.25   $106.30  
  Purchase #5 $127.35   13.252%   $144.2264   $144.23   $144.25   $144.20  
  Purchase #6 $201.52   7.272%   $216.1745   $216.17   $216.15   $216.20  
  Purchase #7 $25.74   7.704%   $27.723   $27.72   $27.70   $27.70  
  7 purchase totals = $938.08       $1,021.7749   $1,021.76   $1,021.75   $1,021.80