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 $24.44   8.526%   $26.5238   $26.52   $26.50   $26.50  
  Purchase #2 $157.64   8.213%   $170.587   $170.59   $170.60   $170.60  
  Purchase #3 $8.53   8.867%   $9.2864   $9.29   $9.30   $9.30  
  Purchase #4 $211.80   8.835%   $230.5125   $230.51   $230.50   $230.50  
  Purchase #5 $52.32   4.492%   $54.6702   $54.67   $54.65   $54.70  
  Purchase #6 $175.92   10.244%   $193.9412   $193.94   $193.95   $193.90  
  Purchase #7 $120.82   8.256%   $130.7949   $130.79   $130.80   $130.80  
  7 purchase totals = $751.47       $816.3160   $816.31   $816.30   $816.30