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 $140.25   7.326%   $150.5247   $150.52   $150.50   $150.50  
  Purchase #2 $214.83   12.129%   $240.8867   $240.89   $240.90   $240.90  
  Purchase #3 $246.90   10.870%   $273.738   $273.74   $273.75   $273.70  
  Purchase #4 $60.77   7.282%   $65.1953   $65.20   $65.20   $65.20  
  Purchase #5 $171.71   9.534%   $188.0808   $188.08   $188.10   $188.10  
  Purchase #6 $111.93   3.818%   $116.2035   $116.20   $116.20   $116.20  
  Purchase #7 $7.95   5.243%   $8.3668   $8.37   $8.35   $8.40  
  7 purchase totals = $954.34       $1,042.9958   $1,043.00   $1,043.00   $1,043.00