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 $191.65   7.589%   $206.1943   $206.19   $206.20   $206.20  
  Purchase #2 $26.81   12.854%   $30.2562   $30.26   $30.25   $30.30  
  Purchase #3 $127.99   9.351%   $139.9583   $139.96   $139.95   $140.00  
  Purchase #4 $218.85   8.655%   $237.7915   $237.79   $237.80   $237.80  
  Purchase #5 $238.34   12.111%   $267.2054   $267.21   $267.20   $267.20  
  Purchase #6 $110.60   8.631%   $120.1459   $120.15   $120.15   $120.10  
  Purchase #7 $8.89   8.498%   $9.6455   $9.65   $9.65   $9.60  
  7 purchase totals = $923.13       $1,011.1971   $1,011.21   $1,011.20   $1,011.20