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 $182.80   8.108%   $197.6214   $197.62   $197.60   $197.60  
  Purchase #2 $209.65   7.159%   $224.6588   $224.66   $224.65   $224.70  
  Purchase #3 $144.71   11.427%   $161.246   $161.25   $161.25   $161.20  
  Purchase #4 $82.46   3.656%   $85.4747   $85.47   $85.45   $85.50  
  Purchase #5 $149.28   9.509%   $163.475   $163.48   $163.50   $163.50  
  Purchase #6 $136.29   3.759%   $141.4131   $141.41   $141.40   $141.40  
  Purchase #7 $22.77   8.179%   $24.6324   $24.63   $24.65   $24.60  
  7 purchase totals = $927.96       $998.5214   $998.52   $998.50   $998.50