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 $72.76   5.173%   $76.5239   $76.52   $76.50   $76.50  
  Purchase #2 $238.63   10.741%   $264.2612   $264.26   $264.25   $264.30  
  Purchase #3 $175.32   11.547%   $195.5642   $195.56   $195.55   $195.60  
  Purchase #4 $161.31   10.231%   $177.8136   $177.81   $177.80   $177.80  
  Purchase #5 $92.80   4.468%   $96.9463   $96.95   $96.95   $96.90  
  Purchase #6 $160.34   4.753%   $167.961   $167.96   $167.95   $168.00  
  Purchase #7 $227.46   13.356%   $257.8396   $257.84   $257.85   $257.80  
  7 purchase totals = $1,128.62       $1,236.9098   $1,236.90   $1,236.85   $1,236.90