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 $48.85   11.238%   $54.3398   $54.34   $54.35   $54.30  
  Purchase #2 $184.76   10.435%   $204.0397   $204.04   $204.05   $204.00  
  Purchase #3 $146.95   12.711%   $165.6288   $165.63   $165.65   $165.60  
  Purchase #4 $92.85   12.393%   $104.3569   $104.36   $104.35   $104.40  
  Purchase #5 $151.48   6.346%   $161.0929   $161.09   $161.10   $161.10  
  Purchase #6 $139.34   10.315%   $153.7129   $153.71   $153.70   $153.70  
  Purchase #7 $149.83   7.476%   $161.0313   $161.03   $161.05   $161.00  
  7 purchase totals = $914.06       $1,004.2023   $1,004.20   $1,004.25   $1,004.10