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 $185.86   11.773%   $207.7413   $207.74   $207.75   $207.70  
  Purchase #2 $58.44   10.503%   $64.578   $64.58   $64.60   $64.60  
  Purchase #3 $201.88   10.207%   $222.4859   $222.49   $222.50   $222.50  
  Purchase #4 $56.34   10.801%   $62.4253   $62.43   $62.45   $62.40  
  Purchase #5 $34.34   13.818%   $39.0851   $39.09   $39.10   $39.10  
  Purchase #6 $231.70   11.689%   $258.7834   $258.78   $258.80   $258.80  
  Purchase #7 $96.88   12.449%   $108.9406   $108.94   $108.95   $108.90  
  7 purchase totals = $865.44       $964.0396   $964.05   $964.15   $964.00