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 $19.48   12.113%   $21.8396   $21.84   $21.85   $21.80  
  Purchase #2 $136.68   8.794%   $148.6996   $148.70   $148.70   $148.70  
  Purchase #3 $250.55   8.835%   $272.6861   $272.69   $272.70   $272.70  
  Purchase #4 $73.90   7.463%   $79.4152   $79.42   $79.40   $79.40  
  Purchase #5 $96.77   10.424%   $106.8573   $106.86   $106.85   $106.90  
  Purchase #6 $43.43   9.316%   $47.4759   $47.48   $47.50   $47.50  
  Purchase #7 $166.33   10.818%   $184.3236   $184.32   $184.30   $184.30  
  7 purchase totals = $787.14       $861.2973   $861.31   $861.30   $861.30