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 $131.52   10.556%   $145.4033   $145.40   $145.40   $145.40  
  Purchase #2 $58.55   5.729%   $61.9043   $61.90   $61.90   $61.90  
  Purchase #3 $73.61   12.393%   $82.7325   $82.73   $82.75   $82.70  
  Purchase #4 $54.63   10.694%   $60.4721   $60.47   $60.45   $60.50  
  Purchase #5 $212.80   6.649%   $226.9491   $226.95   $226.95   $226.90  
  Purchase #6 $232.29   7.214%   $249.0474   $249.05   $249.05   $249.00  
  Purchase #7 $164.95   6.797%   $176.1617   $176.16   $176.15   $176.20  
  7 purchase totals = $928.35       $1,002.6704   $1,002.66   $1,002.65   $1,002.60