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 $157.78   9.525%   $172.8085   $172.81   $172.80   $172.80  
  Purchase #2 $224.61   11.334%   $250.0673   $250.07   $250.05   $250.10  
  Purchase #3 $48.76   6.701%   $52.0274   $52.03   $52.05   $52.00  
  Purchase #4 $208.69   4.584%   $218.2563   $218.26   $218.25   $218.30  
  Purchase #5 $164.57   4.565%   $172.0826   $172.08   $172.10   $172.10  
  Purchase #6 $204.68   6.708%   $218.4099   $218.41   $218.40   $218.40  
  Purchase #7 $10.96   6.266%   $11.6468   $11.65   $11.65   $11.60  
  7 purchase totals = $1,020.05       $1,095.2988   $1,095.31   $1,095.30   $1,095.30