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 $211.84   10.255%   $233.5642   $233.56   $233.55   $233.60  
  Purchase #2 $227.94   3.105%   $235.0175   $235.02   $235.00   $235.00  
  Purchase #3 $34.77   6.485%   $37.0248   $37.02   $37.00   $37.00  
  Purchase #4 $30.58   5.803%   $32.3546   $32.35   $32.35   $32.40  
  Purchase #5 $218.58   6.107%   $231.9287   $231.93   $231.95   $231.90  
  Purchase #6 $182.54   3.301%   $188.5656   $188.57   $188.55   $188.60  
  Purchase #7 $224.36   12.427%   $252.2412   $252.24   $252.25   $252.20  
  7 purchase totals = $1,130.61       $1,210.6966   $1,210.69   $1,210.65   $1,210.70