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 $75.38   11.337%   $83.9258   $83.93   $83.95   $83.90  
  Purchase #2 $148.26   4.554%   $155.0118   $155.01   $155.00   $155.00  
  Purchase #3 $194.36   8.493%   $210.867   $210.87   $210.85   $210.90  
  Purchase #4 $73.37   5.851%   $77.6629   $77.66   $77.65   $77.70  
  Purchase #5 $213.36   12.154%   $239.2918   $239.29   $239.30   $239.30  
  Purchase #6 $235.52   4.221%   $245.4613   $245.46   $245.45   $245.50  
  Purchase #7 $82.57   3.219%   $85.2279   $85.23   $85.25   $85.20  
  7 purchase totals = $1,022.82       $1,097.4485   $1,097.45   $1,097.45   $1,097.50