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 $202.41   13.804%   $230.3507   $230.35   $230.35   $230.40  
  Purchase #2 $33.85   11.541%   $37.7566   $37.76   $37.75   $37.80  
  Purchase #3 $237.52   9.724%   $260.6164   $260.62   $260.60   $260.60  
  Purchase #4 $55.48   10.447%   $61.276   $61.28   $61.30   $61.30  
  Purchase #5 $19.34   6.209%   $20.5408   $20.54   $20.55   $20.50  
  Purchase #6 $61.78   11.174%   $68.6833   $68.68   $68.70   $68.70  
  Purchase #7 $72.42   9.827%   $79.5367   $79.54   $79.55   $79.50  
  7 purchase totals = $682.80       $758.7605   $758.77   $758.80   $758.80