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 $61.57   5.654%   $65.0512   $65.05   $65.05   $65.10  
  Purchase #2 $121.72   13.653%   $138.3384   $138.34   $138.35   $138.30  
  Purchase #3 $27.43   13.615%   $31.1646   $31.16   $31.15   $31.20  
  Purchase #4 $142.37   8.533%   $154.5184   $154.52   $154.50   $154.50  
  Purchase #5 $214.65   4.156%   $223.5709   $223.57   $223.55   $223.60  
  Purchase #6 $41.71   3.578%   $43.2024   $43.20   $43.20   $43.20  
  Purchase #7 $183.35   13.631%   $208.3424   $208.34   $208.35   $208.30  
  7 purchase totals = $792.80       $864.1883   $864.18   $864.15   $864.20