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 $53.79   7.182%   $57.6532   $57.65   $57.65   $57.70  
  Purchase #2 $210.91   10.245%   $232.5177   $232.52   $232.50   $232.50  
  Purchase #3 $77.78   9.860%   $85.4491   $85.45   $85.45   $85.40  
  Purchase #4 $140.41   7.800%   $151.362   $151.36   $151.35   $151.40  
  Purchase #5 $40.77   6.817%   $43.5493   $43.55   $43.55   $43.50  
  Purchase #6 $21.25   12.723%   $23.9536   $23.95   $23.95   $24.00  
  Purchase #7 $235.88   10.237%   $260.027   $260.03   $260.05   $260.00  
  7 purchase totals = $780.79       $854.5119   $854.51   $854.50   $854.50