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 $61.97   12.813%   $69.9102   $69.91   $69.90   $69.90  
  Purchase #2 $178.93   6.510%   $190.5783   $190.58   $190.60   $190.60  
  Purchase #3 $195.39   7.163%   $209.3858   $209.39   $209.40   $209.40  
  Purchase #4 $132.42   13.791%   $150.682   $150.68   $150.70   $150.70  
  Purchase #5 $150.78   11.243%   $167.7322   $167.73   $167.75   $167.70  
  Purchase #6 $125.76   9.443%   $137.6355   $137.64   $137.65   $137.60  
  Purchase #7 $225.27   9.436%   $246.5265   $246.53   $246.55   $246.50  
  7 purchase totals = $1,070.52       $1,172.4505   $1,172.46   $1,172.55   $1,172.40