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 $88.64   8.676%   $96.3304   $96.33   $96.35   $96.30  
  Purchase #2 $61.30   6.384%   $65.2134   $65.21   $65.20   $65.20  
  Purchase #3 $168.47   7.849%   $181.6932   $181.69   $181.70   $181.70  
  Purchase #4 $151.27   9.563%   $165.736   $165.74   $165.75   $165.70  
  Purchase #5 $35.70   11.441%   $39.7844   $39.78   $39.80   $39.80  
  Purchase #6 $49.50   12.315%   $55.5959   $55.60   $55.60   $55.60  
  Purchase #7 $80.34   8.209%   $86.9351   $86.94   $86.95   $86.90  
  7 purchase totals = $635.22       $691.2884   $691.29   $691.35   $691.20