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 $46.32   3.453%   $47.9194   $47.92   $47.90   $47.90  
  Purchase #2 $43.30   9.793%   $47.5404   $47.54   $47.55   $47.50  
  Purchase #3 $79.68   4.611%   $83.354   $83.35   $83.35   $83.40  
  Purchase #4 $215.37   5.489%   $227.1917   $227.19   $227.20   $227.20  
  Purchase #5 $184.66   6.493%   $196.65   $196.65   $196.65   $196.70  
  Purchase #6 $235.68   4.237%   $245.6658   $245.67   $245.65   $245.70  
  Purchase #7 $16.96   4.862%   $17.7846   $17.78   $17.80   $17.80  
  7 purchase totals = $821.97       $866.1059   $866.10   $866.10   $866.20