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 $84.63   10.665%   $93.6558   $93.66   $93.65   $93.70  
  Purchase #2 $115.89   8.147%   $125.3316   $125.33   $125.35   $125.30  
  Purchase #3 $88.77   13.786%   $101.0078   $101.01   $101.00   $101.00  
  Purchase #4 $193.59   9.416%   $211.8184   $211.82   $211.80   $211.80  
  Purchase #5 $126.69   8.620%   $137.6107   $137.61   $137.60   $137.60  
  Purchase #6 $135.47   9.489%   $148.3247   $148.32   $148.30   $148.30  
  Purchase #7 $145.59   12.474%   $163.7509   $163.75   $163.75   $163.80  
  7 purchase totals = $890.63       $981.4999   $981.50   $981.45   $981.50