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 $134.85   11.424%   $150.2553   $150.26   $150.25   $150.30  
  Purchase #2 $26.76   3.386%   $27.6661   $27.67   $27.65   $27.70  
  Purchase #3 $31.59   12.363%   $35.4955   $35.50   $35.50   $35.50  
  Purchase #4 $53.97   3.820%   $56.0317   $56.03   $56.05   $56.00  
  Purchase #5 $51.97   13.385%   $58.9262   $58.93   $58.95   $58.90  
  Purchase #6 $19.83   12.636%   $22.3357   $22.34   $22.35   $22.30  
  Purchase #7 $43.36   5.411%   $45.7062   $45.71   $45.70   $45.70  
  7 purchase totals = $362.33       $396.4167   $396.44   $396.45   $396.40