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 $209.31   11.430%   $233.2341   $233.23   $233.25   $233.20  
  Purchase #2 $68.51   5.138%   $72.03   $72.03   $72.05   $72.00  
  Purchase #3 $200.28   12.801%   $225.9178   $225.92   $225.90   $225.90  
  Purchase #4 $183.33   10.151%   $201.9398   $201.94   $201.95   $201.90  
  Purchase #5 $240.88   13.711%   $273.9071   $273.91   $273.90   $273.90  
  Purchase #6 $225.68   12.693%   $254.3256   $254.33   $254.35   $254.30  
  Purchase #7 $85.50   8.122%   $92.4443   $92.44   $92.45   $92.40  
  7 purchase totals = $1,213.49       $1,353.7987   $1,353.80   $1,353.85   $1,353.60