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 $194.85   10.432%   $215.1768   $215.18   $215.20   $215.20  
  Purchase #2 $229.57   7.446%   $246.6638   $246.66   $246.65   $246.70  
  Purchase #3 $16.91   4.799%   $17.7215   $17.72   $17.70   $17.70  
  Purchase #4 $223.95   3.227%   $231.1769   $231.18   $231.20   $231.20  
  Purchase #5 $239.30   3.106%   $246.7327   $246.73   $246.75   $246.70  
  Purchase #6 $41.87   13.447%   $47.5003   $47.50   $47.50   $47.50  
  Purchase #7 $248.55   6.361%   $264.3603   $264.36   $264.35   $264.40  
  7 purchase totals = $1,195.00       $1,269.3323   $1,269.33   $1,269.35   $1,269.40