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 $235.51   7.290%   $252.6787   $252.68   $252.70   $252.70  
  Purchase #2 $56.95   4.727%   $59.642   $59.64   $59.65   $59.60  
  Purchase #3 $13.27   12.217%   $14.8912   $14.89   $14.90   $14.90  
  Purchase #4 $182.31   5.356%   $192.0745   $192.07   $192.05   $192.10  
  Purchase #5 $222.43   4.609%   $232.6818   $232.68   $232.70   $232.70  
  Purchase #6 $34.51   11.648%   $38.5297   $38.53   $38.55   $38.50  
  Purchase #7 $156.68   6.814%   $167.3562   $167.36   $167.35   $167.40  
  7 purchase totals = $901.66       $957.8541   $957.85   $957.90   $957.90