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 $169.73   11.361%   $189.013   $189.01   $189.00   $189.00  
  Purchase #2 $186.69   11.253%   $207.6982   $207.70   $207.70   $207.70  
  Purchase #3 $30.78   4.122%   $32.0488   $32.05   $32.05   $32.00  
  Purchase #4 $140.85   13.533%   $159.9112   $159.91   $159.90   $159.90  
  Purchase #5 $96.90   12.436%   $108.9505   $108.95   $108.95   $109.00  
  Purchase #6 $61.45   4.145%   $63.9971   $64.00   $64.00   $64.00  
  Purchase #7 $134.72   13.128%   $152.406   $152.41   $152.40   $152.40  
  7 purchase totals = $821.12       $914.0248   $914.03   $914.00   $914.00