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 $211.65   13.846%   $240.9551   $240.96   $240.95   $241.00  
  Purchase #2 $17.33   12.182%   $19.4411   $19.44   $19.45   $19.40  
  Purchase #3 $44.84   13.565%   $50.9225   $50.92   $50.90   $50.90  
  Purchase #4 $116.94   4.167%   $121.8129   $121.81   $121.80   $121.80  
  Purchase #5 $62.28   10.832%   $69.0262   $69.03   $69.05   $69.00  
  Purchase #6 $113.57   3.734%   $117.8107   $117.81   $117.80   $117.80  
  Purchase #7 $184.56   11.658%   $206.076   $206.08   $206.10   $206.10  
  7 purchase totals = $751.17       $826.0445   $826.05   $826.05   $826.00