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 $188.89   11.174%   $209.9966   $210.00   $210.00   $210.00  
  Purchase #2 $78.81   4.501%   $82.3572   $82.36   $82.35   $82.40  
  Purchase #3 $33.35   11.563%   $37.2063   $37.21   $37.20   $37.20  
  Purchase #4 $54.50   4.727%   $57.0762   $57.08   $57.10   $57.10  
  Purchase #5 $151.97   5.146%   $159.7904   $159.79   $159.80   $159.80  
  Purchase #6 $15.52   10.203%   $17.1035   $17.10   $17.10   $17.10  
  Purchase #7 $66.70   3.516%   $69.0452   $69.05   $69.05   $69.00  
  7 purchase totals = $589.74       $632.5754   $632.59   $632.60   $632.60