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 $56.49   12.759%   $63.6976   $63.70   $63.70   $63.70  
  Purchase #2 $82.32   7.662%   $88.6274   $88.63   $88.65   $88.60  
  Purchase #3 $87.66   3.716%   $90.9174   $90.92   $90.90   $90.90  
  Purchase #4 $68.96   5.447%   $72.7163   $72.72   $72.70   $72.70  
  Purchase #5 $7.37   11.200%   $8.1954   $8.20   $8.20   $8.20  
  Purchase #6 $201.34   8.595%   $218.6452   $218.65   $218.65   $218.60  
  Purchase #7 $140.37   12.577%   $158.0243   $158.02   $158.00   $158.00  
  7 purchase totals = $644.51       $700.8236   $700.84   $700.80   $700.70