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 $132.52   11.666%   $147.9798   $147.98   $148.00   $148.00  
  Purchase #2 $207.69   13.534%   $235.7988   $235.80   $235.80   $235.80  
  Purchase #3 $71.92   8.255%   $77.857   $77.86   $77.85   $77.90  
  Purchase #4 $100.95   10.582%   $111.6325   $111.63   $111.65   $111.60  
  Purchase #5 $89.48   3.157%   $92.3049   $92.30   $92.30   $92.30  
  Purchase #6 $161.85   13.481%   $183.669   $183.67   $183.65   $183.70  
  Purchase #7 $154.44   3.842%   $160.3736   $160.37   $160.35   $160.40  
  7 purchase totals = $918.85       $1,009.6156   $1,009.61   $1,009.60   $1,009.70