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 $165.90   12.596%   $186.7968   $186.80   $186.80   $186.80  
  Purchase #2 $77.88   7.743%   $83.9102   $83.91   $83.90   $83.90  
  Purchase #3 $249.78   6.228%   $265.3363   $265.34   $265.35   $265.30  
  Purchase #4 $106.64   13.803%   $121.3595   $121.36   $121.35   $121.40  
  Purchase #5 $52.40   12.515%   $58.9579   $58.96   $58.95   $59.00  
  Purchase #6 $75.66   13.607%   $85.9551   $85.96   $85.95   $86.00  
  Purchase #7 $195.82   4.193%   $204.0307   $204.03   $204.05   $204.00  
  7 purchase totals = $924.08       $1,006.3465   $1,006.36   $1,006.35   $1,006.40