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 $126.68   11.758%   $141.575   $141.58   $141.60   $141.60  
  Purchase #2 $189.26   6.388%   $201.3499   $201.35   $201.35   $201.30  
  Purchase #3 $245.91   9.733%   $269.8444   $269.84   $269.85   $269.80  
  Purchase #4 $243.87   6.453%   $259.6069   $259.61   $259.60   $259.60  
  Purchase #5 $124.91   9.775%   $137.12   $137.12   $137.10   $137.10  
  Purchase #6 $57.50   6.675%   $61.3381   $61.34   $61.35   $61.30  
  Purchase #7 $188.36   12.651%   $212.1894   $212.19   $212.20   $212.20  
  7 purchase totals = $1,176.49       $1,283.0237   $1,283.03   $1,283.05   $1,282.90