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 $132.55   12.140%   $148.6416   $148.64   $148.65   $148.60  
  Purchase #2 $144.36   13.554%   $163.9266   $163.93   $163.95   $163.90  
  Purchase #3 $161.61   12.534%   $181.8662   $181.87   $181.85   $181.90  
  Purchase #4 $70.98   10.324%   $78.308   $78.31   $78.30   $78.30  
  Purchase #5 $61.81   11.648%   $69.0096   $69.01   $69.00   $69.00  
  Purchase #6 $240.45   13.648%   $273.2666   $273.27   $273.25   $273.30  
  Purchase #7 $202.56   4.226%   $211.1202   $211.12   $211.10   $211.10  
  7 purchase totals = $1,014.32       $1,126.1388   $1,126.15   $1,126.10   $1,126.10