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 $55.93   9.739%   $61.377   $61.38   $61.40   $61.40  
  Purchase #2 $118.68   10.817%   $131.5176   $131.52   $131.50   $131.50  
  Purchase #3 $9.66   5.504%   $10.1917   $10.19   $10.20   $10.20  
  Purchase #4 $124.78   8.163%   $134.9658   $134.97   $134.95   $135.00  
  Purchase #5 $117.76   3.518%   $121.9028   $121.90   $121.90   $121.90  
  Purchase #6 $175.56   6.450%   $186.8836   $186.88   $186.90   $186.90  
  Purchase #7 $53.68   9.837%   $58.9605   $58.96   $58.95   $59.00  
  7 purchase totals = $656.05       $705.7990   $705.80   $705.80   $705.90