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 $55.48   13.142%   $62.7712   $62.77   $62.75   $62.80  
  Purchase #2 $228.59   3.213%   $235.9346   $235.93   $235.95   $235.90  
  Purchase #3 $170.87   6.334%   $181.6929   $181.69   $181.70   $181.70  
  Purchase #4 $26.58   13.292%   $30.113   $30.11   $30.10   $30.10  
  Purchase #5 $191.61   3.362%   $198.0519   $198.05   $198.05   $198.10  
  Purchase #6 $116.43   5.153%   $122.4296   $122.43   $122.45   $122.40  
  Purchase #7 $225.70   5.813%   $238.8199   $238.82   $238.80   $238.80  
  7 purchase totals = $1,015.26       $1,069.8131   $1,069.80   $1,069.80   $1,069.80