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 $32.26   13.616%   $36.6525   $36.65   $36.65   $36.70  
  Purchase #2 $194.33   3.657%   $201.4366   $201.44   $201.45   $201.40  
  Purchase #3 $78.25   6.203%   $83.1038   $83.10   $83.10   $83.10  
  Purchase #4 $223.34   5.338%   $235.2619   $235.26   $235.25   $235.30  
  Purchase #5 $221.48   9.737%   $243.0455   $243.05   $243.05   $243.00  
  Purchase #6 $112.45   13.522%   $127.6555   $127.66   $127.65   $127.70  
  Purchase #7 $80.71   6.662%   $86.0869   $86.09   $86.10   $86.10  
  7 purchase totals = $942.82       $1,013.2427   $1,013.25   $1,013.25   $1,013.30