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 $117.91   12.103%   $132.1806   $132.18   $132.20   $132.20  
  Purchase #2 $168.48   13.758%   $191.6595   $191.66   $191.65   $191.70  
  Purchase #3 $84.43   11.866%   $94.4485   $94.45   $94.45   $94.40  
  Purchase #4 $125.93   6.835%   $134.5373   $134.54   $134.55   $134.50  
  Purchase #5 $99.99   7.754%   $107.7432   $107.74   $107.75   $107.70  
  Purchase #6 $86.52   8.771%   $94.1087   $94.11   $94.10   $94.10  
  Purchase #7 $240.70   11.387%   $268.1085   $268.11   $268.10   $268.10  
  7 purchase totals = $923.96       $1,022.7863   $1,022.79   $1,022.80   $1,022.70