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 $138.62   9.736%   $152.116   $152.12   $152.10   $152.10  
  Purchase #2 $250.63   6.278%   $266.3646   $266.36   $266.35   $266.40  
  Purchase #3 $245.91   7.847%   $265.2066   $265.21   $265.20   $265.20  
  Purchase #4 $125.58   6.559%   $133.8168   $133.82   $133.80   $133.80  
  Purchase #5 $66.99   6.870%   $71.5922   $71.59   $71.60   $71.60  
  Purchase #6 $136.95   6.461%   $145.7983   $145.80   $145.80   $145.80  
  Purchase #7 $83.39   10.359%   $92.0284   $92.03   $92.05   $92.00  
  7 purchase totals = $1,048.07       $1,126.9229   $1,126.93   $1,126.90   $1,126.90