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 $246.93   10.597%   $273.0972   $273.10   $273.10   $273.10  
  Purchase #2 $22.28   11.397%   $24.8193   $24.82   $24.80   $24.80  
  Purchase #3 $38.94   7.780%   $41.9695   $41.97   $41.95   $42.00  
  Purchase #4 $158.70   5.576%   $167.5491   $167.55   $167.55   $167.50  
  Purchase #5 $198.85   9.170%   $217.0845   $217.08   $217.10   $217.10  
  Purchase #6 $113.76   9.462%   $124.524   $124.52   $124.50   $124.50  
  Purchase #7 $234.63   5.222%   $246.8824   $246.88   $246.90   $246.90  
  7 purchase totals = $1,014.09       $1,095.9260   $1,095.92   $1,095.90   $1,095.90