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 $59.86   10.148%   $65.9346   $65.93   $65.95   $65.90  
  Purchase #2 $223.27   13.229%   $252.8064   $252.81   $252.80   $252.80  
  Purchase #3 $20.61   8.444%   $22.3503   $22.35   $22.35   $22.40  
  Purchase #4 $57.47   4.357%   $59.974   $59.97   $59.95   $60.00  
  Purchase #5 $213.45   8.828%   $232.2934   $232.29   $232.30   $232.30  
  Purchase #6 $131.66   3.162%   $135.8231   $135.82   $135.80   $135.80  
  Purchase #7 $101.46   3.212%   $104.7189   $104.72   $104.70   $104.70  
  7 purchase totals = $807.78       $873.9007   $873.89   $873.85   $873.90