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 $110.30   7.492%   $118.5637   $118.56   $118.55   $118.60  
  Purchase #2 $231.57   8.481%   $251.2095   $251.21   $251.20   $251.20  
  Purchase #3 $5.41   9.699%   $5.9347   $5.93   $5.95   $5.90  
  Purchase #4 $103.96   5.343%   $109.5146   $109.51   $109.50   $109.50  
  Purchase #5 $22.28   3.314%   $23.0184   $23.02   $23.00   $23.00  
  Purchase #6 $234.83   3.564%   $243.1993   $243.20   $243.20   $243.20  
  Purchase #7 $208.85   8.229%   $226.0363   $226.04   $226.05   $226.00  
  7 purchase totals = $917.20       $977.4765   $977.47   $977.45   $977.40