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 $78.41   6.720%   $83.6792   $83.68   $83.70   $83.70  
  Purchase #2 $64.63   5.551%   $68.2176   $68.22   $68.20   $68.20  
  Purchase #3 $129.71   6.835%   $138.5757   $138.58   $138.60   $138.60  
  Purchase #4 $211.29   8.744%   $229.7652   $229.77   $229.75   $229.80  
  Purchase #5 $30.70   6.109%   $32.5755   $32.58   $32.60   $32.60  
  Purchase #6 $246.56   8.716%   $268.0502   $268.05   $268.05   $268.10  
  Purchase #7 $218.25   9.738%   $239.5032   $239.50   $239.50   $239.50  
  7 purchase totals = $979.55       $1,060.3666   $1,060.38   $1,060.40   $1,060.50