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 $232.31   7.619%   $250.0097   $250.01   $250.00   $250.00  
  Purchase #2 $77.81   12.593%   $87.6086   $87.61   $87.60   $87.60  
  Purchase #3 $186.79   5.553%   $197.1624   $197.16   $197.15   $197.20  
  Purchase #4 $27.95   6.774%   $29.8433   $29.84   $29.85   $29.80  
  Purchase #5 $28.87   6.183%   $30.655   $30.66   $30.65   $30.70  
  Purchase #6 $45.74   11.190%   $50.8583   $50.86   $50.85   $50.90  
  Purchase #7 $165.77   9.550%   $181.601   $181.60   $181.60   $181.60  
  7 purchase totals = $765.24       $827.7383   $827.74   $827.70   $827.80