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 $191.54   13.839%   $218.0472   $218.05   $218.05   $218.00  
  Purchase #2 $55.32   9.656%   $60.6617   $60.66   $60.65   $60.70  
  Purchase #3 $239.83   6.610%   $255.6828   $255.68   $255.70   $255.70  
  Purchase #4 $244.98   10.338%   $270.306   $270.31   $270.30   $270.30  
  Purchase #5 $240.75   3.302%   $248.6996   $248.70   $248.70   $248.70  
  Purchase #6 $70.80   4.190%   $73.7665   $73.77   $73.75   $73.80  
  Purchase #7 $52.56   11.617%   $58.6659   $58.67   $58.65   $58.70  
  7 purchase totals = $1,095.78       $1,185.8297   $1,185.84   $1,185.80   $1,185.90