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 $149.25   5.572%   $157.5662   $157.57   $157.55   $157.60  
  Purchase #2 $217.85   10.834%   $241.4519   $241.45   $241.45   $241.50  
  Purchase #3 $54.66   8.859%   $59.5023   $59.50   $59.50   $59.50  
  Purchase #4 $162.63   5.126%   $170.9664   $170.97   $170.95   $171.00  
  Purchase #5 $177.65   11.278%   $197.6854   $197.69   $197.70   $197.70  
  Purchase #6 $163.57   11.256%   $181.9814   $181.98   $182.00   $182.00  
  Purchase #7 $45.26   12.747%   $51.0293   $51.03   $51.05   $51.00  
  7 purchase totals = $970.87       $1,060.1829   $1,060.19   $1,060.20   $1,060.30