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 $208.51   12.401%   $234.3673   $234.37   $234.35   $234.40  
  Purchase #2 $216.62   13.724%   $246.3489   $246.35   $246.35   $246.30  
  Purchase #3 $246.83   6.822%   $263.6687   $263.67   $263.65   $263.70  
  Purchase #4 $194.98   4.269%   $203.3037   $203.30   $203.30   $203.30  
  Purchase #5 $169.45   4.343%   $176.8092   $176.81   $176.80   $176.80  
  Purchase #6 $11.70   5.581%   $12.353   $12.35   $12.35   $12.40  
  Purchase #7 $86.72   3.207%   $89.5011   $89.50   $89.50   $89.50  
  7 purchase totals = $1,134.81       $1,226.3519   $1,226.35   $1,226.30   $1,226.40