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 $211.89   11.751%   $236.7892   $236.79   $236.80   $236.80  
  Purchase #2 $158.67   6.392%   $168.8122   $168.81   $168.80   $168.80  
  Purchase #3 $103.31   13.484%   $117.2403   $117.24   $117.25   $117.20  
  Purchase #4 $204.55   3.849%   $212.4231   $212.42   $212.40   $212.40  
  Purchase #5 $194.98   11.557%   $217.5138   $217.51   $217.50   $217.50  
  Purchase #6 $153.30   6.451%   $163.1894   $163.19   $163.20   $163.20  
  Purchase #7 $11.77   7.509%   $12.6538   $12.65   $12.65   $12.70  
  7 purchase totals = $1,038.47       $1,128.6218   $1,128.61   $1,128.60   $1,128.60