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 $91.42   5.360%   $96.3201   $96.32   $96.30   $96.30  
  Purchase #2 $157.84   11.417%   $175.8606   $175.86   $175.85   $175.90  
  Purchase #3 $78.50   5.497%   $82.8151   $82.82   $82.80   $82.80  
  Purchase #4 $8.86   9.773%   $9.7259   $9.73   $9.75   $9.70  
  Purchase #5 $77.44   12.423%   $87.0604   $87.06   $87.05   $87.10  
  Purchase #6 $132.65   4.627%   $138.7877   $138.79   $138.80   $138.80  
  Purchase #7 $29.64   7.805%   $31.9534   $31.95   $31.95   $32.00  
  7 purchase totals = $576.35       $622.5232   $622.53   $622.50   $622.60