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 $26.87   8.383%   $29.1225   $29.12   $29.10   $29.10  
  Purchase #2 $61.89   6.612%   $65.9822   $65.98   $66.00   $66.00  
  Purchase #3 $172.91   11.752%   $193.2304   $193.23   $193.25   $193.20  
  Purchase #4 $45.92   13.427%   $52.0857   $52.09   $52.10   $52.10  
  Purchase #5 $98.65   7.429%   $105.9787   $105.98   $106.00   $106.00  
  Purchase #6 $60.91   4.753%   $63.8051   $63.81   $63.80   $63.80  
  Purchase #7 $182.96   11.410%   $203.8357   $203.84   $203.85   $203.80  
  7 purchase totals = $650.11       $714.0403   $714.05   $714.10   $714.00