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 $68.36   8.592%   $74.2335   $74.23   $74.25   $74.20  
  Purchase #2 $117.93   4.839%   $123.6366   $123.64   $123.65   $123.60  
  Purchase #3 $174.41   4.743%   $182.6823   $182.68   $182.70   $182.70  
  Purchase #4 $154.75   13.164%   $175.1213   $175.12   $175.10   $175.10  
  Purchase #5 $65.85   4.266%   $68.6592   $68.66   $68.65   $68.70  
  Purchase #6 $37.57   7.733%   $40.4753   $40.48   $40.50   $40.50  
  Purchase #7 $63.90   3.320%   $66.0215   $66.02   $66.00   $66.00  
  7 purchase totals = $682.77       $730.8297   $730.83   $730.85   $730.80