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 $46.69   13.107%   $52.8097   $52.81   $52.80   $52.80  
  Purchase #2 $119.95   8.314%   $129.9226   $129.92   $129.90   $129.90  
  Purchase #3 $121.43   4.324%   $126.6806   $126.68   $126.70   $126.70  
  Purchase #4 $74.80   9.721%   $82.0713   $82.07   $82.05   $82.10  
  Purchase #5 $231.50   4.151%   $241.1096   $241.11   $241.10   $241.10  
  Purchase #6 $17.55   9.723%   $19.2564   $19.26   $19.25   $19.30  
  Purchase #7 $184.74   13.493%   $209.667   $209.67   $209.65   $209.70  
  7 purchase totals = $796.66       $861.5172   $861.52   $861.45   $861.60