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 $57.68   5.684%   $60.9585   $60.96   $60.95   $61.00  
  Purchase #2 $240.56   11.339%   $267.8371   $267.84   $267.85   $267.80  
  Purchase #3 $7.41   6.442%   $7.8874   $7.89   $7.90   $7.90  
  Purchase #4 $169.93   7.437%   $182.5677   $182.57   $182.55   $182.60  
  Purchase #5 $47.97   4.178%   $49.9742   $49.97   $49.95   $50.00  
  Purchase #6 $24.75   3.118%   $25.5217   $25.52   $25.50   $25.50  
  Purchase #7 $77.81   5.384%   $81.9993   $82.00   $82.00   $82.00  
  7 purchase totals = $626.11       $676.7459   $676.75   $676.70   $676.80