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 $218.74   11.811%   $244.5754   $244.58   $244.60   $244.60  
  Purchase #2 $49.92   11.653%   $55.7372   $55.74   $55.75   $55.70  
  Purchase #3 $235.29   6.582%   $250.7768   $250.78   $250.80   $250.80  
  Purchase #4 $175.45   5.517%   $185.1296   $185.13   $185.15   $185.10  
  Purchase #5 $178.71   11.331%   $198.9596   $198.96   $198.95   $199.00  
  Purchase #6 $37.47   6.861%   $40.0408   $40.04   $40.05   $40.00  
  Purchase #7 $23.54   9.225%   $25.7116   $25.71   $25.70   $25.70  
  7 purchase totals = $919.12       $1,000.9310   $1,000.94   $1,001.00   $1,000.90