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 $10.62   12.230%   $11.9188   $11.92   $11.90   $11.90  
  Purchase #2 $71.82   5.348%   $75.6609   $75.66   $75.65   $75.70  
  Purchase #3 $42.85   3.241%   $44.2388   $44.24   $44.25   $44.20  
  Purchase #4 $101.80   10.708%   $112.7007   $112.70   $112.70   $112.70  
  Purchase #5 $30.30   4.819%   $31.7602   $31.76   $31.75   $31.80  
  Purchase #6 $218.32   13.396%   $247.5661   $247.57   $247.55   $247.60  
  Purchase #7 $199.73   13.721%   $227.135   $227.14   $227.15   $227.10  
  7 purchase totals = $675.44       $750.9805   $750.99   $750.95   $751.00