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 $202.81   4.184%   $211.2956   $211.30   $211.30   $211.30  
  Purchase #2 $233.71   5.553%   $246.6879   $246.69   $246.70   $246.70  
  Purchase #3 $227.59   3.300%   $235.1005   $235.10   $235.10   $235.10  
  Purchase #4 $120.84   4.787%   $126.6246   $126.62   $126.60   $126.60  
  Purchase #5 $58.41   11.308%   $65.015   $65.02   $65.00   $65.00  
  Purchase #6 $239.94   5.572%   $253.3095   $253.31   $253.30   $253.30  
  Purchase #7 $18.97   13.526%   $21.5359   $21.54   $21.55   $21.50  
  7 purchase totals = $1,102.27       $1,159.5690   $1,159.58   $1,159.55   $1,159.50