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 $45.69   13.126%   $51.6873   $51.69   $51.70   $51.70  
  Purchase #2 $190.86   8.274%   $206.6518   $206.65   $206.65   $206.70  
  Purchase #3 $159.39   10.270%   $175.7594   $175.76   $175.75   $175.80  
  Purchase #4 $210.76   12.772%   $237.6783   $237.68   $237.70   $237.70  
  Purchase #5 $80.96   9.483%   $88.6374   $88.64   $88.65   $88.60  
  Purchase #6 $168.73   7.161%   $180.8128   $180.81   $180.80   $180.80  
  Purchase #7 $197.52   5.317%   $208.0221   $208.02   $208.00   $208.00  
  7 purchase totals = $1,053.91       $1,149.2491   $1,149.25   $1,149.25   $1,149.30