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 $52.83   11.757%   $59.0412   $59.04   $59.05   $59.00  
  Purchase #2 $91.79   10.629%   $101.5464   $101.55   $101.55   $101.50  
  Purchase #3 $203.53   11.120%   $226.1625   $226.16   $226.15   $226.20  
  Purchase #4 $34.74   6.115%   $36.8644   $36.86   $36.85   $36.90  
  Purchase #5 $218.32   8.713%   $237.3422   $237.34   $237.35   $237.30  
  Purchase #6 $215.54   6.466%   $229.4768   $229.48   $229.50   $229.50  
  Purchase #7 $215.29   6.280%   $228.8102   $228.81   $228.80   $228.80  
  7 purchase totals = $1,032.04       $1,119.2437   $1,119.24   $1,119.25   $1,119.20