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 $24.94   3.136%   $25.7221   $25.72   $25.70   $25.70  
  Purchase #2 $193.44   4.835%   $202.7928   $202.79   $202.80   $202.80  
  Purchase #3 $146.79   10.310%   $161.924   $161.92   $161.90   $161.90  
  Purchase #4 $160.76   9.240%   $175.6142   $175.61   $175.60   $175.60  
  Purchase #5 $132.86   3.570%   $137.6031   $137.60   $137.60   $137.60  
  Purchase #6 $118.96   4.646%   $124.4869   $124.49   $124.50   $124.50  
  Purchase #7 $134.85   6.125%   $143.1096   $143.11   $143.10   $143.10  
  7 purchase totals = $912.60       $971.2527   $971.24   $971.20   $971.20