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 $232.80   5.818%   $246.3443   $246.34   $246.35   $246.30  
  Purchase #2 $84.44   3.640%   $87.5136   $87.51   $87.50   $87.50  
  Purchase #3 $181.41   11.334%   $201.971   $201.97   $201.95   $202.00  
  Purchase #4 $145.70   5.652%   $153.935   $153.94   $153.95   $153.90  
  Purchase #5 $182.82   7.662%   $196.8277   $196.83   $196.85   $196.80  
  Purchase #6 $40.54   11.621%   $45.2512   $45.25   $45.25   $45.30  
  Purchase #7 $122.53   7.703%   $131.9685   $131.97   $131.95   $132.00  
  7 purchase totals = $990.24       $1,063.8113   $1,063.81   $1,063.80   $1,063.80