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 $223.67   12.648%   $251.9598   $251.96   $251.95   $252.00  
  Purchase #2 $18.92   3.438%   $19.5705   $19.57   $19.55   $19.60  
  Purchase #3 $79.43   3.278%   $82.0337   $82.03   $82.05   $82.00  
  Purchase #4 $58.77   4.453%   $61.387   $61.39   $61.40   $61.40  
  Purchase #5 $229.82   3.412%   $237.6615   $237.66   $237.65   $237.70  
  Purchase #6 $34.67   8.742%   $37.7009   $37.70   $37.70   $37.70  
  Purchase #7 $181.71   6.404%   $193.3467   $193.35   $193.35   $193.30  
  7 purchase totals = $826.99       $883.6601   $883.66   $883.65   $883.70