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 $227.43   6.274%   $241.699   $241.70   $241.70   $241.70  
  Purchase #2 $179.89   3.494%   $186.1754   $186.18   $186.20   $186.20  
  Purchase #3 $235.29   6.331%   $250.1862   $250.19   $250.20   $250.20  
  Purchase #4 $167.56   5.282%   $176.4105   $176.41   $176.40   $176.40  
  Purchase #5 $70.37   4.463%   $73.5106   $73.51   $73.50   $73.50  
  Purchase #6 $39.74   8.664%   $43.1831   $43.18   $43.20   $43.20  
  Purchase #7 $33.45   8.497%   $36.2922   $36.29   $36.30   $36.30  
  7 purchase totals = $953.73       $1,007.4570   $1,007.46   $1,007.50   $1,007.50