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 $31.49   11.190%   $35.0137   $35.01   $35.00   $35.00  
  Purchase #2 $115.33   8.254%   $124.8493   $124.85   $124.85   $124.80  
  Purchase #3 $53.35   8.741%   $58.0133   $58.01   $58.00   $58.00  
  Purchase #4 $168.96   8.193%   $182.8029   $182.80   $182.80   $182.80  
  Purchase #5 $247.26   10.419%   $273.022   $273.02   $273.00   $273.00  
  Purchase #6 $147.26   9.298%   $160.9522   $160.95   $160.95   $161.00  
  Purchase #7 $131.79   4.360%   $137.536   $137.54   $137.55   $137.50  
  7 purchase totals = $895.44       $972.1894   $972.18   $972.15   $972.10