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 $160.69   8.655%   $174.5977   $174.60   $174.60   $174.60  
  Purchase #2 $53.92   10.730%   $59.7056   $59.71   $59.70   $59.70  
  Purchase #3 $53.41   8.210%   $57.795   $57.80   $57.80   $57.80  
  Purchase #4 $24.59   12.767%   $27.7294   $27.73   $27.75   $27.70  
  Purchase #5 $134.94   8.156%   $145.9457   $145.95   $145.95   $145.90  
  Purchase #6 $38.84   7.551%   $41.7728   $41.77   $41.75   $41.80  
  Purchase #7 $182.82   8.334%   $198.0562   $198.06   $198.05   $198.10  
  7 purchase totals = $649.21       $705.6024   $705.62   $705.60   $705.60