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 $162.76   11.845%   $182.0389   $182.04   $182.05   $182.00  
  Purchase #2 $99.64   13.233%   $112.8254   $112.83   $112.85   $112.80  
  Purchase #3 $33.98   13.140%   $38.445   $38.45   $38.45   $38.40  
  Purchase #4 $160.70   4.110%   $167.3048   $167.30   $167.30   $167.30  
  Purchase #5 $223.27   13.148%   $252.6255   $252.63   $252.65   $252.60  
  Purchase #6 $155.60   7.558%   $167.3602   $167.36   $167.35   $167.40  
  Purchase #7 $200.32   6.233%   $212.8059   $212.81   $212.80   $212.80  
  7 purchase totals = $1,036.27       $1,133.4057   $1,133.42   $1,133.45   $1,133.30