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 $52.53   12.467%   $59.0789   $59.08   $59.10   $59.10  
  Purchase #2 $186.54   3.329%   $192.7499   $192.75   $192.75   $192.70  
  Purchase #3 $80.85   5.420%   $85.2321   $85.23   $85.25   $85.20  
  Purchase #4 $229.89   4.781%   $240.881   $240.88   $240.90   $240.90  
  Purchase #5 $182.92   11.117%   $203.2552   $203.26   $203.25   $203.30  
  Purchase #6 $102.83   3.436%   $106.3632   $106.36   $106.35   $106.40  
  Purchase #7 $11.96   8.807%   $13.0133   $13.01   $13.00   $13.00  
  7 purchase totals = $847.52       $900.5736   $900.57   $900.60   $900.60