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 $235.87   11.564%   $263.146   $263.15   $263.15   $263.10  
  Purchase #2 $173.56   8.346%   $188.0453   $188.05   $188.05   $188.00  
  Purchase #3 $130.63   3.492%   $135.1916   $135.19   $135.20   $135.20  
  Purchase #4 $26.97   9.810%   $29.6158   $29.62   $29.60   $29.60  
  Purchase #5 $52.93   13.273%   $59.9554   $59.96   $59.95   $60.00  
  Purchase #6 $157.83   7.498%   $169.6641   $169.66   $169.65   $169.70  
  Purchase #7 $102.78   13.373%   $116.5248   $116.52   $116.50   $116.50  
  7 purchase totals = $880.57       $962.1430   $962.15   $962.10   $962.10