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 $117.98   7.355%   $126.6574   $126.66   $126.65   $126.70  
  Purchase #2 $47.87   10.577%   $52.9332   $52.93   $52.95   $52.90  
  Purchase #3 $218.29   6.230%   $231.8895   $231.89   $231.90   $231.90  
  Purchase #4 $235.99   12.831%   $266.2699   $266.27   $266.25   $266.30  
  Purchase #5 $29.25   6.377%   $31.1153   $31.12   $31.10   $31.10  
  Purchase #6 $226.50   6.512%   $241.2497   $241.25   $241.25   $241.20  
  Purchase #7 $93.70   6.641%   $99.9226   $99.92   $99.90   $99.90  
  7 purchase totals = $969.58       $1,050.0376   $1,050.04   $1,050.00   $1,050.00