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 $87.55   5.832%   $92.6559   $92.66   $92.65   $92.70  
  Purchase #2 $191.57   4.735%   $200.6408   $200.64   $200.65   $200.60  
  Purchase #3 $180.36   5.181%   $189.7045   $189.70   $189.70   $189.70  
  Purchase #4 $69.78   10.205%   $76.901   $76.90   $76.90   $76.90  
  Purchase #5 $231.40   3.628%   $239.7952   $239.80   $239.80   $239.80  
  Purchase #6 $237.87   3.316%   $245.7578   $245.76   $245.75   $245.80  
  Purchase #7 $144.65   6.228%   $153.6588   $153.66   $153.65   $153.70  
  7 purchase totals = $1,143.18       $1,199.1140   $1,199.12   $1,199.10   $1,199.20