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 $157.44   12.361%   $176.9012   $176.90   $176.90   $176.90  
  Purchase #2 $22.54   9.811%   $24.7514   $24.75   $24.75   $24.80  
  Purchase #3 $163.45   3.805%   $169.6693   $169.67   $169.65   $169.70  
  Purchase #4 $244.52   3.356%   $252.7261   $252.73   $252.75   $252.70  
  Purchase #5 $61.82   9.724%   $67.8314   $67.83   $67.85   $67.80  
  Purchase #6 $201.91   8.687%   $219.4499   $219.45   $219.45   $219.40  
  Purchase #7 $107.43   9.120%   $117.2276   $117.23   $117.25   $117.20  
  7 purchase totals = $959.11       $1,028.5569   $1,028.56   $1,028.60   $1,028.50