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 $206.52   3.629%   $214.0146   $214.01   $214.00   $214.00  
  Purchase #2 $137.35   11.785%   $153.5367   $153.54   $153.55   $153.50  
  Purchase #3 $234.45   7.766%   $252.6574   $252.66   $252.65   $252.70  
  Purchase #4 $55.62   7.361%   $59.7142   $59.71   $59.70   $59.70  
  Purchase #5 $34.84   3.119%   $35.9267   $35.93   $35.95   $35.90  
  Purchase #6 $192.97   11.866%   $215.8678   $215.87   $215.85   $215.90  
  Purchase #7 $85.49   11.453%   $95.2812   $95.28   $95.30   $95.30  
  7 purchase totals = $947.24       $1,026.9986   $1,027.00   $1,027.00   $1,027.00