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 $127.83   11.855%   $142.9842   $142.98   $143.00   $143.00  
  Purchase #2 $179.86   12.282%   $201.9504   $201.95   $201.95   $202.00  
  Purchase #3 $50.44   3.669%   $52.2906   $52.29   $52.30   $52.30  
  Purchase #4 $216.96   13.132%   $245.4512   $245.45   $245.45   $245.50  
  Purchase #5 $172.63   11.725%   $192.8709   $192.87   $192.85   $192.90  
  Purchase #6 $224.66   11.841%   $251.262   $251.26   $251.25   $251.30  
  Purchase #7 $43.44   12.642%   $48.9317   $48.93   $48.95   $48.90  
  7 purchase totals = $1,015.82       $1,135.7410   $1,135.73   $1,135.75   $1,135.90